DISCUSSION
The potentiality of pollen grains as an important system in higher plants
has been well realized in both functional and reproductive biology
(Mascarenhas, 1990; Mc Cormic, 1991, 1993; Bedinger, 1992). As an organ
which is considered to be less influenced by changing ecological conditions,
the characters of pollen grains are regarded as a more dependable and useful
tool in studies of comparative morphology that lead to conclusions in plant
taxonomy, phylogeny and evolution than those of any other single vegetative
part (Saad, 1971; Nair, 1974a). Biostratigraphy using dispersed pollen, spores
and other microfossils must be used to establish relative ages (Doyle, 2001).
Pollen, the core of the reproductive machinery, constitutes the resultant
repository
of
the
evolutionary
processes
consisting
of
variations,
recombination and selection during the plant's life cycle (Nair, 1980a). The
morphological characters of pollen grains are those relating to the germinal
aperture, exine ornamentation, exine strata, size and shape of which the
aperture character is considered to be of primary importance, exine surface
pattern secondary and the others as tertiary (Nair, 196513). The aperture
characters are based on their form, number and distribution, and they show
variation in different plants at various taxonomic levels so as to be of use in
the identification of genera, species and varieties. Several palynologists have
focused their attention on the aperture in a phylogenetic consideration
(Kuprianova, 1948; Nair, 1970a., 1974a; Walker, 1976). The exine surface
patterns often serve as supplementary factors to the apertural form in
reaching taxonomic and phylogenetic conclusions (Erdtman, 1952; Nair.
1970a). The morphoform categorization based on ornamentation of exine is
particularly useful in stenopalynous taxa, but the tertiary characters like exine
strata, size and shape are of very little value in applied taxonomy due to their
least phylogenetic significance.
1. MORPHOLOGICAL ANALYSIS
Morphological analysis of pollen grains is made based mainly on the
aperture character. The other palynological characters such as exine
ornamentation, exine strata, pollen size and shape are also taken into
consideration as supplementary factors. Based on the palynological study
made here on members of the order Malvales from the South Indian region a
brief discussion of the different palynological characters of the group is made,
and in addition aspects such as pollen morphological evolution, dimorphism of
pollen grains and pollen morphology in the systematics and phylogeny of the
order are also considered.
(a) Aperture morphoform
The apertures are specially delimited and generally thin walled areas in
the outer pollen wall through which the pollen tube usually, but not always
emerges at the time of germination. Generally palynological discussions are
based on the position of the aperture, their number and form. In a
phylogenetic-evolutionary context the most significant feature of pollen
aperture is that they are not located randomly on the surface of the pollen
grain, but usually have very definite placement with reference to the grain's
pole and equator defined by its position in the pollen tetrad (Walker, 1973;
Harley and Baker, 2001). Proximal, distal, zonal, and global are considered to
be the hierarchical order of evolutionary progress with regard to the position of
the aperture (Nair, 1970b). In some pollen the aperture areas are as thick or
thicker than the exine, and therefore apertures may act as a weak point of
rupture during germination of pollen grain (Walker and Doyle. 1975).
Based on the presence or absence of aperture the pollen grains are
divided into two types, the aperturate and inaperturate types. The number of
aperture may vary from one to many, and their position is proximal, distal,
equatorial or global (Nair, 1991), of which the zonal and global ones are
restricted to the angiosperms. The number and distribution of aperture in the
pollen grain forms one among many trends in the evolution of pollen
morphology (Walker and Doyle, 1975; Van Campo, 1976). An evolutionary
sequence from simple to more complex apertural types has been illustrated
by Chanda et a/. (1979). Increase in number from primitive to advanced
appears to be the general trend. The pollen grains of monocots usually have
one aperture and those in dicots usually three. Apertures serve other
functions like harmomegathy in pollen grains subjected to the changes in
humidity (Wodehouse, 1935; Payne, 1972) and as exit sites for the proteins
which function in the recognition reaction between pollen grain and stigma
(Heslop-Harrison, 1971).
The form of aperture is either elongate (colpate) or circular (porate)
along with intermediary types (Nair, 196513). The variants of the colpate and
porate forms are colporate, pororate, spiraperturate and synaperturate, etc.
Phylogenetically furrows (colpate) are apparently the primitive form, and the
pores must have become differentiated later by the process of contraction and
diminution of the length of the colpus. In the colporate forms ectocolpium is
incongruent with the endocolpium, of which the latter is either faintly marked
(colporoidate) or well defined (colporate). Sub categorization of this basic
aperture morphoform may be made on the basis of the nature and form of the
endoapertures. The important configurations based on the endoapertures are
circular, lalongate and lolongate. The aperture number has some correlation
with the life expectancy of the pollen (Dajoz e t a / . , 1992).
A survey of the palynological data of the presently studied taxa of the
family Malvaceae showed pantoporate, 6-zonoporate, pantocolporate and 3zonocolporate forms in varying frequencies. From the data it is found that
pantoporate condition shows overwhelming preponderance (Table. 2, Text
Fig.l), these conditions being present in 63 out of 77 taxa studied (16 genera.
4 tribes). The other forms are of very low incidence, especially the 3-
zonocolporate, pantocolporate, 6-zonoporate condition which were observed
only in one genus each. The 3-colporate condition is found in 9 species and
two rnorphotypes of Abutilon under the tribe Malveae, although grain with an
increase in number of colpi are also observed in two taxa of the genus
Thespesia, under the tribe Gossypieae. 6-zonoporate condition is found in 3
taxa of the genus Gossypium under the tribe Gossypieae. The frequencies of
distribution of pantoporate, 6-zonoporate, pantocolporate and 3-zonocolporate
condition observed were in 63, 3, 2 and 9 species respectively. In addition,
pantoporate condition was observed in 9 morphotypes
and 3-zonocolporate
in two rnorphotypes.
TABLE. 2. DISTRIBUTION OF APERTURE MORPHOFORM
IN THE FAMILY MALVACEAE.
Tribe
G
S
1
2
G
S
Decaschistieae
Gossypieae
-
-
Hibisceae
4
29+5'
Malvavisceae
4
6+1'
Malveae
7
25+3'
1
3
--
* Morphotype G r ~ e n u s S - Species
With regard to the position of aperture, the pores are scattered on the
surface of the grain in the pantoporate condition. In the Malvaceae, pores are
Text Fig .I.
Frequency distribution of aperture
forms in IVlalvaceae
Pantoporate
1
Tribe
6-zanoporate
Pantocolporate
3-zonocolporate
Genera R! Species E Morphotype I
large and circular. In the 6-zonoporate condition the pores are arranged in
rows of 3 each in either poles of the grain. Khan (1992) reported the pollen
grains of the Thespesia group are of colporate nature. In the colporate forms
the ectocolpium is narrow and faintly demarcated (brevicolpate) and the
endocolpium is well formed, and circular in nature and distributed in the zonal
position (Table. 3 and Text Fig.2).
Pollen morphology of Malvaceae has been worked out by Banerji
(1929); Sayeeduddin et a/. (1942); Erdtman (1952); Nair (1958, 61, and 62);
Prasad (1963); Chaudhuri and Mallik (1965). Sharma and Rastogi (1965);
Vilasini et a/. (1966); Ganguly and Chanda (1974); Srivastava (1982);
Christensen (1986); Khan (1992); Lan et a/. (1995); Germano et a1.(1997);
Pandeya et a/. (1997).
1
~~~:~~~
1
1
-1
TABLE. 3. DISTRIBUTION OF ORA IN MALVACEAE
Tribe
PantcJporate
Pore (circular)
Endocolpium
7
6-zon;porate
(pore circular)
.-
Decaschistieae
.
Gossypieae
Hibisceae
Malvavisceae
.. ~.
-
Malveae
--
Text Fig.2. Frequency distribution of ora
in Malvaceae
Pantoporate
Colporate
6-zonoporate
1 13Tribe R Genera C1 Species Q Mor~hoty~e
1
Pollen grains in the presently investigated taxa of the family
Bornbacaceae are all 3-aperturate types.. The frequencies of the major
apertural types (colpate, colporate) observed in the present group show that
colporate one was the predominant type occurring in 3 species and 1
morphotype (3 tribes and 3 genera), while one species found to be colpate in
nature (Table.4 and Text Fig.3). With regard to the position of the aperture all
the species had zonal position. In the colporate forms the endocolpia were
either circular, lalongate or lolongate of which circular one was found to be the
dominant type represented by two species under two different genera and
tribes. Lalongate and lolongate configurations were found in one species each
(lalongate is found in the morphotype) (Table 5 and Text Fig. 4). Ceiba
pentandra possess both lalongate and circular ora.
Pollen morphology of the family Bombacaceae was studied earlier by
Tsukada (1964); Fuchs (1967) and Robyns (1971). They have supported the
separation of the family Bombacaceae from the Malvaceae on the basis of
palynomorphological characteristics. But in the present study only three tribes
were taken in to account due the rare representation of genera in South India.
TABLE. 4. DISTRIBUTION OF APERTURE FORMS IN SOUTH INDIAN
BOMBACACEAE.
r-Gneae
* Morphotype
denus
.
G-
- SpeGGs
TABLE 5 . DISTRIBUTION OF VARIOUS TYPES OF ORA IN
SOUTH INDIAN BOMBACACEAE.
Adansonieae
Ceibeae
1
1
1
1
(
l
1
1'
1
Durioneae
-
The Sterculiaceous grains in the present study showed aperture
number varying from 3 to 5. The three aperture morphoforms are the most
frequently occurring type in the family, although grains with increase in
number of colpi were observed (4 - 5 colporate) only in one genus Waltheria
Text Fig. 3. Distribution of aperture form
in Bombacaceae
3 - cot pate
/
Tribe
Genera
3 - colporate
Species I3Morphotype]
Text Fig.4. Frequency distribution of ora
in Bornbacaceae
Lolongate
Circular
talongate
1 ElTribe ElGenera El Species ElMorphotype /
(Tribe Hermannieae) (Table. 6, Text Fig. 5). Palynological data obtained from
the present study of the South Indian Sterculiaceae revealed different
apertural types such as 3-colpate, 3-colporate, 4 - 5 colporate, 3-porate and .
3-pororate. Out of the five tribes only one was stenopalynous with ~ - Z O ~ O
porate condition (Helictereae, 3 genera and 5 species). In Sterculieae and
Buttnerieae both colpate and colporate conditions co-exist. In Dombeyeae
porate and pororate conditions were observed. The distribution of various
aperture rnorphoforms are 3 -zono colpate (4 species, 3 genera and 2 tribes),
3-zonocolporate (14 Species, 6 genera and 3 tribes), 4-5 zonocolporate
(2 Species, I genera and 7 tribe), 3 -zonoporate (6 Species, 4 Genera and
2 tribes), 3-zonopororate (3 species, 1 genera and 1 tribe).
The important configurations based on the endo aperture of the family
were circular, lalongate and faint, of which the lalongate condition was found
to be dominant (Table. 7 and Text Fig. 6). Circular type was observed in 4
species (4 genera and 2 tribes) while lalongate in 8 species (4 genera and 2
tribes). In 4 species (3 genera and 2 tribe) the endocolpium is found to be
faint. In porate and pororate condition the pores were circular. With regard to
the aperture, zonal position was found in all taxa investigated. Similar variation in
the endoaperture characters has been previously reported in Euphorbiaceae
(Khan, 1968); Rubiaceae (Mathew and Philip, 1983); Acanthaceae (Valsaladevi
and Mathew, 1989) and Caesalpeniaceae (George, 1995).
TABLE 6. DISTRIBUTION OF APERTURE FORMS IN
SOUTH INDIAN STERCLILIACEAE
3zono-
1
Tribe
1-.
4
Coiporate
r-.
3 zono3 zono-
~olpate
G
~..
S
G
S
4
10
G
S
G
-.
Sterculieae
1
1
S
G
S
,
I
.-
.
Helictereae
3
5
Dornbeyeae
1
1
Herrnannieae
-
-
Buttnerieae
--
G - Genus
3
1
2
1
2
.-
p~
3
1
1
I
s - species
TABLE 7. DISTRIBUTION OF ORA MORPHOFORM
IN STERCULIACEAE
G - Genus
-s-Species
1
3
Text Fig. 5. Frequency distribution of
aperture form in Sterculiaceae
Cotpate
4-5 zonocolporataonocolporate
3-
1
Porate
~ be
r i I3 ~ e n e k Species
1
Pororate
Text Fig.6. Frequency distribution of ora
in Sterculiaceae
Colporate Colporate Colporate
circular
lalongate
faint
Porate
circular
Pornrate
circular
Pollen morphology of Sterculiaceae was reported earlier by (Rao,
1950; Martin, 1967; Sharma, 1967; Kohler, 1976; Bahadur and Reddy, 1977;
Bahadur and Srikanth, 1983). In Helicteres dimorphism in aperture
morphoform was attributed to some set back in the cytological phenomenon
(Sharma, 1967).
Presently investigated taxa of Tiliaceae show only colporate aperture
form. The family was stenopalynous with 3 colporate grains under the 3 tribes
studied (5 genera, 25 species and 4 morphotype) (Table 8 and Text Fig. 7).
The important configurations based on the endoaperture of the family
are circular, lalongate or lolongate and it is found that the circular and
lalongate configurations are the dominating types (Table 9, Text Fig 8). The
circular type is found in 11 species and one morphotype (2 genera, 2 tribe)
while the lalongate type in 12 species and 2 morphotype (4 genera, 2 tribes).
Lolongate condition was observed in 2 species (1 Genera). In 1 morphotype
the endocolpiurn is faint. Palynological studies on the family Tiliaceae were
attempted earlier (Banerjee, 1933; Datta, 1956; Patel and Datta, 1958; Datta
and Panda, 1961; Datta and Roy, 1963; Datta and Bose, 1964; Chaudhuri
and Mallick, 1965; Chaudhari, 1965; Barnzai and Randhawa, 1965; Datta and
Mukhopadhyay, 1969; Sharma. 1969; Chambers and Godwin, 1971).
Text Fig. 7. Frequency distributrion of
aperture morphoform in Tiliaceae
Cofporate
1 Q ~ r i b eCJ Genera
Species
Morphotype
I
Text Fig.8. Frequency distribution of ora
in Tiliaceae
Circular
talongate
Lolongate
Faint
TABLE 8. DIFFERENT APERTURE MORPHOFORMS IN TILIACEAE
Colporate (3-zonocolporate)
Trrbe
-
S
-
Brownlowieae
-
-
2
1
Grewieae
18+3*
-
Tilieae
* Morphotype G - Genus
S - Species
TABLE 9. DIFFERENT TYPES OF ORA IN TILIACEAE.
I Lalongate
Circular
Tribe
- G ~ s -
Lolongate
Faint
G
Brownlowieae
--
-
Grewieae
2
8+1*
Tilieae
2
4+1*
.-
* Morphotype G - Genus
.-
S - Species
(B) EXlNE SURFACE PATTERN
The pattern of pollen wall sculpturing is species specific, and pointed
out to be determined by the sporophyte (Quiros, 1975). Blueprints for different
sculpturing patterns are laid down at the time of meiosis while the tetrads are
still encased in the callose wall (Takahashi. 1993). The architecture of pollen
wall provides a number of phylogenitically useful characters, among which the
exine stratification, structure and type of sculpturing appear to be basic.
Surface
ornamentation
of
exine
is considered
to
be a significant
morphological character helping a great deal in the categorization of various
genera and species in the case of stenopalynous families, and as a
supplementary factor in eurypalynous families (Nair and Sharma, 1965).
Pollen wall of most angiosperms constitute two fundamentally different
layers, the inner intine and the outer exine. Outer wall is composed of a
highly resistant material, the sporopollenin. Sculpturing in semitectate and
intectate pollen of primitive angiosperm (Ranalian complex) appears to be
homologous with previously existing sculptures in tectate grains (Walker,
1974). The exine ornamentation types fall into two broad categories, the
depression type, [Psilate (smooth), reticulate, foveolate (pitted), scarbiculate
(with fine projection), fossulate (grooved) and striate] which were advanced,
and the projection or excrescence type [spinulate, spinate, baculate, clavate,
verrucate (warthy), tuberculate and granulate] which were comparatively
primitive. But it is difficult to ascertain this because of their mixed occurrence
in related taxa. A perusal of the literature clearly unfolds the significance of
this character in taxonomic and phylogenetic discussions (Erdtman, 1952;
Ferguson and Webb, 1970; Chambers and Godwin, 1971; Hebda and Lott,
1973; Skvarla et a/., 1976; Graham and Barker, 1981; Vezey, 1990; Vezey
and Skvarla, 1990; Klitgaard, 1991; Sharma and Saran, 1992; Nilsson, 1992;
Nowicke, 1994; Khan, 1994,1995 and Murthy, 1996).
Pollen grains of Malvaceae are typified by having excrescence on the
ectine surface and are of diagnostic value in the delimitation of genera and
species. The height of the spine varies in different members
of genera and
species itself and this helps in the identification and separation of species and
morphotypes.
Different
developmental
stages
have
provided
useful
information on the exine pattern differentiation in Hibiscus rosa-sinensis
(Chaturvedi and Datta, 1984). Lan et a/. (1995) studied the structural features
of pollen wall in Gossypiurn hirsutuin. L. Germano et a/. (1997) reported the
pollen wall development in Malvastrurn corchorifoliurn and observed that
Malvastrurn is highly specialized and evolutionarily advanced due to its spine
morphology, long spines with pointed apices and prominent basal cushions.
Pandeya et a/. (1997) made a comparative study of pollen of Sida
hemitropousa and Sida acuta and reported that the micro characters of
sporoderm differ considerably.
Different types of ornamentations are observed in the interspinal
region and are categorized in Table. 10 and Text Fig.9. Among this the
predominantly occurring type is the granulose form, which was found in 5
tribes (17 genera. 65 species and 9 morphotypes). Foveolate was found in 3
tribes (6 genera, and 12 species and 2 morphotype). Pollen dimorphism is
recorded in Oldenlandia urnbellata by Bir Bahadur (1964) and in Farmea by
Muller (1969). Banerjee (1929): Erdtman (1952); Nair (1958); Gupta and Roy
(1970) have noted dimorphism in the Malvaceae in the nature of spines, i.e.,
some spines are short with obtuse ends and others comparatively longer and
acute. Pollen grains with and without spines have been reported in some
families by Rao and Ong (1971) and Ong and Rao (1973).
TABLE 10. DIFFERENT ORNAMENTATION TYPES IN MALVACEAE
Granulose
Tribe
Foveolate
Decaschistieae
Gossypieae
Hibisceae
1
4
)
2515.
1
6+1*
Malvavisceae
(
4
Malveae
1
6
L
* Morphotype G - Genus
/
1
1
1
I
1
4
1
I
1
~
27+3'
4
7+2'
1
-2
S - Species
In the present investigation members of Bombacaceae possess the
depression type of ornamentation with predominance of reticulate pattern (2
tribe, 2 genera, 3 species and one morphotype) and foveolate condition being
present in 1 species (1 genera, ltribe). In the reticulate pattern the network
may be heterobrochate or homobronchate (Table. 11 and Text Fig. 10). In
Ceibeae ornamentation is heterobrochate, showing smaller network (muri)
seen on the margins of the colpus and larger muri away from the colpus. In
Vigna unguiculata the exine surface is coarsely reticulate with high muri.
Text Fig. 9.Frequency distribution of
ornamentation in Malvaceae
Granulose
10
~ r i b e13Genera Q Species
Foveolate
Morphotype I
TABLE 11. DIFFERENT ORNAMENTATION TYPE IN BOMBACACEAE
Tribe
_.?"i""",-I~"lates~
Cei beae
Durioneae
* Morphotype G - Genus S - Species
The ornamentation patterns of Sterculiaceae shows that majority of the
taxa had sculptured grains. The depression type (reticulate and foveolate)
and excrescence type (spinate and granulate) are the two broad categories of
ornamentation forms in the case of sculptured grains, of which the depression
type is the predominant one. Reticulate pattern was observed in 11 species.
7 genera, and 3 tribes. Foveolate pattern 'was observed in 9 species, 6 genera.
and 4 tribe (Table. 12, Text Fig. 11). In 4 species (2 genera, 2 tribes) the
network pattern is very faint. Granulate type was observed in 5 species
4 genera and 2 tribes. In some Sterculiaceous members like Pterospermum,
Dombeya and Melhania mixed type of ornamentation was observed, where
the exine is ornamented with
small spines and the inter spinal region found
to be granulose or foveolate. SEM study reveals that small papillae are
present on the exine surface of Helicteres along with finely granulate type of
ornamentation and this support the view of Sharma (1967)
Text Fig.10. Frequency distribution of
ornamentation type in Bornbacaceae
Reticulate
/ Q Tribe
Foveolate
Genera Kl Species El Morphotype /
Table.12 Different ornamentation i n Sterculiaceae
Tribe
Faintly
reticulate
Reticulate
G
G
S
3
5
-.
S
Granulate
Foveolate
G
G
S
2
3
2
3
S
... .~
Sterculieae
1
3
2
Helictereae
~~.
Dombeyeae
2
Buttnerieae
;- Genus
S - Species
The present data in the Tiliaceae show that majority of the taxa had
sculptured grains (Table. 13, Text Fig.12). In the depression type, reticulate
pattern was common (2 tribes, 2 genera, 10 species, and 2 morphotypes) and
faintly reticulate was observed in 2 tribes, 3 genera, 7 species and
1 morphotype. Retipilate was observed in 1 tribe, 2 genera and 5 species.
Foveolate was observed in 3 tribes, 3 genera, 3 species and 1 morphotype.
Pollen morphology of Tiliaceae in relation to plant Taxonomy was studied in
detail by Sharma (1969) and reported that majority of the members posses
reticulate pattern.
Text Fig.lI.Frequency distribution of
ornamentation type in Sterculiaceae
Faintly reticulate
Reticulate
Granulate
Foveolate
Text Fig.12.Frequency distribution of ornamentation
type in Tiliaceae
Faintly reticulate
Reticulate
Retipilate
Foveolate
TABLE 13. DIFFERENT TYPES OF ORNAMENTATION IN TILIACEAE
Tribe
reticulate
Reticulate
Retipilate
Foveolate
Brownlowieae
Tilieae
3+1'
L
* Morphotype G - Genus S - Species
(c) Exine stratification
Exine stratification refers to the different layers (strata) present in the
pollen wall (Nair, 1964). The pollen wall is made up of two layers, the inner
intine and outer exine. Exine consists of two layers, the inner homogeneous
non-sculptured (nexine syn. Endine) .and the outer variously sculptured
(sexine syn. Ectine) layer. The exine is composed of highly resistant material
called sporopollenin, which has been of great value to sample the plant
community present at any particular time (Rudramuniyappa, 1995). An
intermediate third layer, the medine between the exine and intine (Saad, 1972)
and a peripheral layer (perine) in ferns (Nair, 1965a) was reported. The exine is
also known to be associated with the mode of pollination (Knox, 1984). Exine
stratification studies in the Mimoseae (Guinet, 1981; Niezgoda eta/., 1983; Feuer
et a/., 1985) and Caesalpiniaceae (Ferguson, 1980, 1987; Patel et a/., 1985;
Crepet and Taylor, 1986; Ferguson and Pearce, 1986) have described the
importance of the pollen wall strata in discussing their relationships. Ferguson
and Skvarla (1979, 1981, and 1983) have carried out Transmission Electron
Microscopic (TEM) studies on the exine stratification of different Papilionaceous
members. For elucidating the relationships of the group Gnaphalieae (Astraceae)
Breitwieser and Sampson (1997) investigated the exine of several members by
means of Transmission Electron Microscopy. But in the present investigation,
TEM studies could not be carried out.
However, the stratification such as
endoexine and ecto exine could be clearly recognizable in few members
(Lavatera rosea, Althea rosea, Sida species, Melochia species, Dombeya
species, Triumfetta species, Corchorus species and Berrya species).
(d) Pollen size
Pollen size is generally considered as a tertiary character in
phylogenetic studies. Pollen size was found to be an index to chromosome
numerical variations (aneuploidy and polyploidy) and has been shown to be
useful in cytopalynological studies (Maurizio. 1956; Bir and Sidhu, 1980; Bir
and Sagoo, 1981; Sagoo and Bir, 1983; Nair and Ravikumar, 1984;
Ravikumar and Nair, 1985; Saraswathyamma et a/., 1995; Meenakumari ef
a/., 1996). Some earlier investigators have reported large variations in the size
of pollen grains in certain cultivated plants (Rangaswamy, 1935; Mukerjee,
1951; Maurizio, 1956) and they have attributed this difference to polyploidy.
Size variation of pollen grains between diploid and induced tetraploid plants
has been reported by Dnyansgar and Sudhakaran (1972) in Vinca rosea. Ong
and Rao (1973) noted great variations for pollen size due to triploidy or
polyploidy in Wikstroemia viridiflora.
In general pollen polymorphism has
been considered to be due to cytological factors (Tara and Namboothiri,
1976). Size variation in induced tetraploid plants of Tagetis erecta was
reported by Mathew and Mathew (1980).
Sometimes the size or shape of the pollen grains may be useful in
identification,
especially
in unipalynous (stenopalynous) groups. The
extraction processes is also a reason for change in size of the pollen grain.
Grains are swollen to various extents by acetolysis, which depends on the
duration of the treatment (Reitsma, 1969).
Pollen grains were fairly large in Malvaceae, their size ranged from
31(Sida schimperiana) to 136pm (Abelmoschus manihot). Several members
exhibited
pollen
size
dimorphism.
Pollen
grains
of
Bombacaceae,
Sterculiaceae and Tiliaceae were relatively smaller in size. Pollen size of
Bombacaceae ranged from 29 (Bombax ceiba) to 61pm (Bombax
scopulorum). Data of pollen size in various species in different tribes of the
family Sterculiaceae showed a wide range of size variation from 7pm (Cola
acuminata) to 78pm (Dombeya spectabilis). In Tiliaceae the large sized pollen
grains were observed in Grewia bracteata (47pm) and small in Muntingia
calabura (6pm) (Table.1).
(e) Pollen shape
The shape of the pollen is usually unfixed in angiosperms, and hence
this character is not generally considered as a reliable parameter in pollen
morphological analysis in relation to taxonomy and phylogeny (Nair, 1970a).
The pollen shape is affected by the embedding media, and it varies in
different views. Based on the pollen shape, the angiosperm pollen has been
grouped under several classes judged by the PIE ratio (Walker and Doyle,
1975) such as peroblate, oblate, suboblate, oblate-spheroidal, spheroidal.
prolate-spheroidal, subprolate, prolate, and perprolate, of which the
spheroidal shape is considered to be the most basic form, which changes in
either direction.
In the Malvaceae, the pollen grains are spherical in shape except in
one genus Abutilon in which the grains are suboblate. The spheroidal shape
occurs in 5 tribes, 18 genera, 68 species and 9 morphotypes. Sub oblate
grains are found in 1 tribe, 1 genus, 9 species and 2 morphotypes (Table
14,Text Fig.13).
TABLE 14. DISTRIBUTION OF SHAPE IN MALVACEAE
Spheroidal
1
, +++ " .
Suboblate
Decaschistieae
Hibisceae
Malvavisceae
4
Malveae
7
'
6+1*
1
25+3'
9+2'
* Morphotype G - Genus S -Species
In the Bornbacaceae, the grains show different shapes such as oblate
spheroidal and oblate. 'The oblate group is common in the family (2 tribes, 2
genera, 3 species and 1 morphotype) and 1 species show oblate spheroidal
pollen group (Table 15. Text Fig.14).
TABLE 15. DISTRIBUTION OF POLLEN SHAPES IN BOMBACACEAE
Oblate
Oblate spheroidal
Tribe
G
1
1
Adansoniae
Ceibeae
Durioneae
* Morphotype
I
1
I
l
I
1
G - Genus
i
1
S - Species
S
G
S
~
1
I
1
1
2
1+Ie
l
1
Text Fig.43 Frequency distribution of pollen shape
in Malvaceae
Suboblate
Spheroidal
/
Tribe R Genera
Species
Morphotype
/
Text Fig.14. Frequency distribution of
pollen shapes in Bombacaceae
Oblate spheroidal
IIQ~ r i k E, Genera W Species
Obiate
lIMorphotype
I
In the family Sterculiaceae, the pollen grains exhibit all the different
shapes except peroblate and perprolate forms. Spheroidal, oblatespheroidal
and prolate spheroidal are the common types. Among this spheroidal shape
was observed in 4 genera and 8 species. Oblate spheroidal was observed in
5 genera and 6 species. Oblate in 3 genera and 4 species. Prolate spheroidal
was observed in 5 genera and 5 species (Table. 16 and Text Fig.15). Sub
oblate was observed in 1 genus and 1 species. Sub prolate was observed in 1
genus and 2 species and prolate was observed in 3 genera and 3 species
TABLE 16. DISTRIBUTION OF POLLEN SHAPES IN STERCULIACEAE
G - Genus
S - Species
In the family Tiliaceae pollen shapes observed were oblate, sub
prolate, prolate (Table. 17 and Text Fig. 16) of which prolate was the common
shape (2 tribes, 3 genera. 20 species and 4 morphotypes). Oblate shape is
found in 1 tribe. 1 genus and 2 species. Subprolate was reported in 2 tribes, 2
genera and 3 species
Text Fig .15. Frequency distribution of shape
in Sterculiaceae
I!I Tribe HGenera E3 SDecieS I
Text Fig.16. Frequency distribution of
pollen shape in Tiliaceae
Oblate
Subprolate
Prolate
-
V
e
r
a I3Species
Morphotype
1
TABLE 17. DIFFERENT POLLEN SHAPES IN TlLlACEAE
1
k
Oblate
Tribe
Prolate
Subprolate
G
S
G
Grewieae
1
2
2
16+3'
Tilieae
1
1
1
4+1"
Brownlowieae
* Morphotype
G
S
1
2
G - Genus
S - Species
2. Pollen dimorphism
Although the morphology of the pollen grain in angiosperms is fairly
constant in a single species, dimorphism with regard to certain palynological
characters have been known to occur less frequently. The phenomenon of
dimorphism and polymorphism of pollen grains is the occurrence of two or
more pollen morphoforms of the same species, and also occasionally in a
single plant or even with in an anther. (Darwin, 1892) was the first to describe
this phenomenon in angiosperm families, and since then this has been
reported by several others in a number of families like Baker (1956,
1961,1966); Bir Bahadur (1964, 1968); Nair and Sharma (1966. 1967);
Srivastava (1976a); Mathew and Philip (1983); Nair and Ravikumar (1984);
Mathew and Valsaladevi (1989); Koshy and Mathew (1992).
Pollen
dimorphism has been reported to occur naturally or due to various factors
such as ecological conditions, geographical distribution, effect of different
treatments etc. In many cases it has been useful in revealing phylogenetic
and phytogeographical limitation of polymorphic species (Baker, 1956), for
supplementing fragmentary informations available on chromosome numbers
and distribution of cytotypes (Lewis, 1964) and also as an aid of practical
value to plant breeders as it offers a novel means of detecting incompatibility
systems (Lewis, 1956).
In the order Malvales pollen dimorphism has been reported in a few
members by several workers (Nair, 1958, 1961; Davis, 1967; Datta and
Mukhopadhyay. 1969; Gupta and Roy. 1970; Bahadur and Reddy, 1977;
Srivastava, 1982; Bahadur et a/., 1984; Srikanth and Bahadur, 1981.1986;
Bahadur et al., 1996). During the present study dimorphism with respect to
several palynological characters has been not~cedsuch as pollen size, ora
character, aperture number, exine thickness. Trimorphism of pollen grains
with respect to size has been noticed in some members of Malvaceae. In
addition, another dimorphic aspect characterized by colour difference of the
exine after acetolysis has also been detected in few a members of
Malvaceae.
(a) Aperture number
Dimorphism for aperture number of pollen grains is previously known in
a few plants such as Grevillea vestita (Rao, 1964), Schismatoclada
psychotrioidea (Lewis, 1965) and Zea mays (Koul, 1969). In Grevillea, the
number of aperture is reported to be directly proportional to the grain size.
Rao (1964) has attributed pollen dimorphism for aperture number in Grevillea
vestita to genetic factor. Koul (1969), from the evidence of distribution of the
two types of pollen grains in Zea mays suggested that pollen dimorphism in
this plant is under genetic control, and also postulated that the plants of this
species which exhibited dimorphism were heterozygous for the gene
controlling the germ pores, with alleles segregating during division of pollen
mother cells producing pollen grains of two types. In the present study 4 and 5
apertures were observed in Waltheria. It has already been reported that
increased number of aperture is an advanced character and was observed in
all species of Waltheria (Kohler, 1976), thus it representing a model system of
evolution of aperture character and pollen dimorphism.
(b) Ora
The nature and size of the ora is known to be remarkably uniform in a
given species. Reports of pollen dimorphism for this character are too scanty.
Mondal et a/. (1974) have reported dimorphism of ora in the pollen grains of
Desmodium floribundum in which they recognized two different types of ora.
In the present study, dimorphism of ora was observed in Ceiba pentandra,
where it possesses circular ora, while one of its morphotypes exhibited
lalongate ora. Trimorphism with respect to ora was noticed in some members
and in their morphotypes. Grewia nenrosa showed circular ora, while one of
its morphotype showed lalongate ora. In another morphotype the ora is faint.
In Grewia oppositifolia dimorphic ora is observed (lalongate and circular).
Corchorus aestuans possessed circular, while its rnorphotype showed
lalongate ora.
(c) Exine thickness and ornamentation
Dimorphism for exine thickness is relatively a less frequent feature.
Ong and Rao (1973) detected this in a few angiosperm families in which they
have reported a negative correlation between pollen grain size and exine
thickness, the smaller grains showing thicker walls and the larger grains
thinner walls. In the present study also this negative correlation was observed
in Thespesia populnea, Hibiscus surattensis, H.tiliaceus, Sida cordata and
Ceiba pentandra.
The first record of dimorphism for exine ornamentation is by Muller
(1969). During the present study dimorphism for exine ornamentation was
observed in several members. In Abufilon indicurn interspinal region is found
to be foveolate while in its rnorphotype the interspinal region is granulose.
Similar variation of exine pattern in the interspinal region was observed in
Abutilon persicurn (A.persicum rnorphotype I shows granulose while
Morphotype II show foveolate). Sida cordata (rnorphotype I and II) were found
to possess granulose type of exine pattern in the interspinal region while its
morphotype Ill shows foveolate pattern. Sida rnysorensis rnorphotype I and II
show different types of ornamentation pattern i . e foveolate and granulose
respectively. In the Tiliaceae. Grewia newosa show dimorphic exine pattern
(morphotype I and II possess reticulate exine, morphotype Ill possess
foveolate pattern). Reticulate and faintly reticulate pattern was observed in
morphotypes of Corchorus aestuans.
Dimorphic spines are observed in Malva parviflora, Althea rosea and
Malope malacoides by Nair (1958). In Hibiscus, variations have been
recorded with regard to the type of spines, varying from spinate to tuberculate
(Nair, 1961) which provides suggestion on the directions of morphological
evolution of the excrescence. Srivastava (1982) reported excrescence
dirnor~hismin Abelmoschus esculents and Althea rosea.
The excrescence shows marked difference in various grains in size,
shape and tips. The excrescence system bears pointed spines (columnar) as
a general rule, and the other spine Iexcrescence type includes blunt tip
(baculate), curved tip (uncinate), globose (gemmate), areolate and proliferous
forms. Dimorphism with respect to spine character was noticed in several
members of Malvaceae. In Decaschistia crotonifolia, Gossypium barbedence,
Hibiscus hispidissimus, H.micranthus, Abelmoschus angulosus and Fioria
vitifolia either columnar or baculate along with uncinate spines were noticed.
In H, syriacus and Malvaviscus penduliflorus M 11, vericate and baculate
spines were observed. In Abelmoschus esculentus both columnar and
divisibaculate excrescence types were observed. In Hibiscus trionum, Althea
rosea and Malva parviflora dimorphism with respect to height of the spines
(small and long spines) were noticed. Majority of the taxa in Malvaceae
possess either columnar or baculate spines. In the present study the height
and basal diameter of the spine, diameter of the basal cushion (basal cushion
is formed by the union of collumella on which the spine is fixed) and
interspinal distance were measured. The basal cushion is referred as high
and low. Height of the spine is also considered here for the formation of key.
(d) Colour dimorphism
The pollen grains of a few taxa studied here (Hibiscus tiliaceous,
Thespesia populnea, Lavatera rosea) exhibited another dimorphic feature
characterized by colour difference of the exine after the chemical processes of
acetolysis, and this is attributed to the deep staining of the endo exine in
some grains. The phenomenon is termed 'chemical dimorphism' (Mathew and
Philip, 1976) because the difference is noticeable only after the chemical
treatment. Darwin (1892) had made some indication as to the existence of two
natural colour types of pollen grains in Villarsia, the pollen of short-styled
flower of this being bluish and those of the long styled ones yellow.
(e) Grain size
Dimorphism of pollen grains has been noticed in a number of species
in Malvaceae with respect to pollen size (Gossypium barbadense, Thespesia
populnea, Fioria vitifolius Morphotype I and II, Hibiscus canascence,
H.
hispidisirnuss morphotype 4, H. lobatus morphotype II, H. surattensis,
H. tiliaceous, Abelrnoschus rnanihot, Abutilon hybridurn, A. megapotamicum,
Sida acuta, S. cordata 111, S linifolia, S. rhombifolia, S. ravii, S. scabrida). In
the case of dimorphic species, pollen grains could be grouped under 2 size
classes, namely larger grains (LG) and smaller grains (SG), the frequency of
which varied in different species. Pollen trimorphism was found in
Malvaviscus penduliflorus and Lavatera rosea) (Table.I ) .
Ceiba pentandra morphotype I1 (Bombacaceae) possessed size
dimorphism. Davis (1967) reported stamen number and pollen size in levo
and dextro rotatory flowers of Bornbax ceiba. No size dimorphism was
observed in any members of the Sterculiaceae studied. Pollen dimorphism
with respect to heterostyly in Sterculiaceae was reported (Bahadur and
Reddy, 1977; Bahadur et a/., 1984; and Srikanth and Bahadur, 1981.1986).
Clear association between heterostyly and pollen dimorphism in Waltheria
was reported Bahadur et a/. (1996).
In Tiliaceae pollen dimorphism was
reported by Datta and Mukhopadhyay (1969). But in the present study
dimorphism with respect to size was not observed in Tiliaceae.
3. Pollen morphology and Taxonomy
Pollen morphology as a useful tool in solving problems of taxonomy
and also in the recognition, identification and interpretation of relationships of
plants at various taxonomic levels has been stressed by Erdtrnan (1952) and
Nair (1964). The pollen morphology has been applied not only for the
differentiation of sub families and tribes, but also at the generic and species
levels (Bailey and Nast, 1943). The study of pollen morphology on the plants
of Western Himalayan region (Nair 1965b) has provided evidence for its
significance in the taxonomy of the several families. A very elaborate study of
pollen morphology in relation to plant taxonomy of Indian rnonocots has been
reported by Sharma (1967). Exhaustive treatise on pollen morphology in
relation to plant taxonomy have been provided by Bhoj Raj (1961) for
Acanthaceae, Sticx (1960) for Compositae,Punt (1962) and Kohler (1965) for
Euphorbiaceae, Nilsson (1967) for Gentianaceae and Herber (2002) for
Thymelaeaceae.
Pollen investigations have attempted grouping of plant families as
eurypalynous and stenopalynous.
In eurypalynous there are different
morphological types, which form a basis to delimit the taxa comprising the
family, while in the stenopalynous families a single morphological type typifies
the whole family and hence in such cases the demarcation of different taxa on
the basis of pollen morphology may be difficult (Erdtman, 1952). In the case of
eurypalynous families the apertures are considered to be of primary
importance, ornamentations as secondary and the other characters mainly
size to be of tertiary importance. In stenopalynous taxa the apertures are of
the same basic type and hence in such cases the data of secondary and
tertiary characters are significant.
(a) Malvaceae
Palynological data obtained from the present study of South Indian
Malvaceae reveal that the family is eurypalynous with pantoporate, 6 porate,
pantocolporate and 3 colporate types. Nair and Sharma (1962) have
suggested that pollen keys can be used to categorize plants of a family at
various taxonomic level. The present data show that out of the five tribes,
three are stenopalynous having only pantoporate types, and the remaining
two eurypalynous showing different apertural morphoforms.
Stenopalynous tribes:
Decaschistieae
Pantoporate
Hibisceae
Pantoporate
Malvavisceae
Pantoporate
Eurypalynous tribes
Gossypieae
pantocolporate. 6-zonoporate
Malveae
3-zonocolporate, pantoporate
In the case of eurypalynous tribes, further grouping at generic level
may be possible based on aperture character, and the following grouping are
proposed in the two tribes, Gossypieae and Malveae.
Tribe Gossypieae
Grains pantocolporate
Thespesia
Grains 6- zonoporate
Gossypium
Tribe Malveae
Grains 3- zonocolporate
Abutilon
Grains pantoporate
Alcea
Lavatera
Herissantia
Malva
Malvastrum
Modiola
Sida
In the case of a few genera such as Hibiscus, Sida and Abutilon
different species within a genus were found to possess different pollen
morphoforms with respect to secondary and tertiary characters, and the
following grouping are proposed in them.
Decaschistia
Pollen grains pantoporate
Pore circular
Grain shape spheroidal
Exine surface foveolate
D.crotonifolia
Exine surface granulose
Average size above 70pm
Spine longer
D.rufa
Average size below 60prn
Spine shorter
D.trilobata
Gossypium
Pollen grains 6-zonoporate
Pore circular
Exine surface granulose
Grain shape spheroidal
Average size above 100pm
G.barbadense
Average size below 100prn
Pores larger
G. arboreum
Pores smaller
G.herbaceum
Thespesia
Pollen grains pantocolporate
Endocolpium circular
Exine surface granulose
Pollen shape spheroidal
Endocolpium larger
Tpopulnea
(Size dimorphism)
Endocolpium smaller
T lampas
Abelmoschus
Pollen grains pantoporate
Pore circular
Exine surface granulose
Pollen shape spheroidal
Average size above 100pm
Basal cushion not formed
Dimorphic spines
A. angulosus
Basal cushion slightly formed
Size dimorphism
Spine longer
A. manihot
Spine shorter
A. moschatus
Average size below 1OOpm
Dimorphic spines
A. esculentus
Monomorphic spines
A. ficulrleus
Grains pantoporate
Pore circular
Surface granulose
Shape spheroidal
Size dimorphism
Basal cushion slightly formed
Pore smaller
F.vitifolia Morphotype I
Basal cushion not formed
Pore larger
F.vitifolia Morphotype II
Hibiscus
Pollen grains pantoporate
Pore circular
Grain shape spheroidal
Exine surface foveolate
Average size below 70pm
Basal cushion not formed
Basal cushion slightly formed
Average size above 90pm
Basal cushion not formed
Exine surface granulose
Average size below 80pm
Basal cushion not formed
Spine longer
Spine shorter
Dimorphic spines
Basal cushion slightly formed
Spine shorter
Spine longer
Basal cushion well developed
Dimorphic spines
H.hirius
H-lobatus M I
H. trionum
H.lunarifolius
H.schezopetalus
H.radiatus
Monornorphic spines
Average size above 80vm
Basal cushion not formed
Spine longer, above 20pm
Dimorphic spines
Monomorphic spines
H.hispidissirnus M I
H.hispidissirnus M 111
Spine shorter, below 15pm
Dimorphic spines
Acute and curved
Acute and verrcate
Monomorphic spines
Tip acute
Spine shorter
Spine longer
Tip blunt
Size dimorphism
Spine longer
Spine shorter
Basal cushion slightly formed
Pore larger
Pore smaller
Size dimorphism
Spine shorter
H.sreenarayanianus
H.sabdariffa
H.syriacus
H.rosa-sinensis
H.jurca tus
H.platanifolius
H.acetose//a.
H.tiliaceus
H.lobatus M II
H,hispidissmus M IV
H hispidissmus M /I
H.mutabilis
H.surattensis
Kydia
Grains pantoporate
Pore circular
Surface granulose
Shape spheroidal
Average size 50pm
K. calcyna
Malachra
Grains pantoporate
Pore circular
Surface granulose
Shape spheroidal
Average size 86prn
Basal cushion slightly formed
Malvaviscus
Grains pantoporate
Pore circular
Surface granulose
Shape spheroidal
Size trimorphisrn
Spine dimorphism
Pavonia
Grains pantoporate
Pore circular
Surface granulose
Shape spheroidal
Average size between 61-75pm
Urena
Pollen grains pantoporate
Pore circular
Exine surface granulose
Shape spheroidal
Spine longer
Spine shorter
Abutilon
Grains 3-zonocolporate
Ectocolpium narrow and faint
Endocolpium circular
Ectine surface spinate
Shape suboblate
M.capitata
Surface foveolate
Basal cushion not formed
Basal cushion low
Basal cushion high
A.megapotamicum
A.persicum M II
A.indicurn M I
A. neelgeerrense
Surface granulose
Average size above 50pm
Basal cushion not formed
Basal cushion slightly formed
Basal cushion well developed
Average size below 50pm
Basal cushion not formed
Basal cushion slightly formed
Basal cushion well developed
Althaea
Grains pantoporate
Pore cirular
Surface granulose
Shape spheroidal
Average size between 70- 1001~m
Dimorphic spines (long and short)
Lavatera
Grains pantoporate
Pore circular
Surface granulose
Shape spheroidal
Size trimorphism
Herissantia
Grains pantoporate
Pore circular
Surface granulose
Shape spheroidal
Basal cushion well developed
Average size 40pm
A. persicum M I
A. striatum
A.pannosurn
A.rarnosurn
Malva
Pollen grains pantoporate
Pore circular
Surface granulose
Shape spheroidal
Monomorphic spines
Average size 52pm
Dimorphic spines
Average size 42pm
Malvastrum
Grains pantoporate
Pore circular
Surface foveolate
Shape spheroidal
Average size 45pm
Basal cushion well developed
Modiola
Grains pantoporate
Pore circular
Surface foveolate
Shape spheroidal
Average size 35vm
Basal cushion slightly formed
M.caroliniana
Sida
Pollen grains pantoporate
Pore circular
Shape spheroidal
Surface foveolate
Basal cushion high and sharply defined
Pore smaller
S. rnysorensis M. I
Pore larger
S.repens
S. cordata M.Ill
Size dimorphism
Surface granulose
Basal cushion not formed
Pore smaller
S. cuneifolia
Spine longer
Spine shorter
Basal cushion high and sharply defined
Size dimorphism
Spine longer
Spine shorter
Pore larger
S.ravii
S.scabrida
Pore smaller
S. acuta
No size dimorphism
Pore larger
Spine length above 5vm
S. fryxellii
S.cordata I
Spine length between 3 to 4pm
S.spinosa
S.cordifolia
Spine length below 3pm
S.mysorensis M II
S. ovata
Pore smaller
Spine longer
S. linifolia
S.codophia
Spine shorter
S.alnifolia
S.beddornei
(b)Bombacaceae
Out of the three tribes, two are stenopalynous with 3-zonocolporate
grains, and the remaining one eurypalynous showing different apertural
morphoforrns such as 3 -zonocolpate and 3-zonocolporate
Eurypalynous tribe
Adansonieae
Stenopalynous tribes
Ceibeae
Durioneae
Tribe Adansonieae
Grains 3-zonocolpate
Bombax Scopulorurn
Grains 3-zonocolporate
Bombax ceiba
Bombax
Grains 3-zonocolpate
Surface reticulate
Shape oblate
Grains 3-zonocolporate
Endocolpium lolongate
Surface reticulate
Shape oblate
B. ceiba
Ceiba
Grains 3-zonocolporate
Shape oblate
Surface reticulate (heterobrochae)
Endocolpium circular
Endocolpium lalongate
Cullenia
Grains 3-zonocolporate
Endocolpium circular
Surface foveolate
Shape oblate spheroidal
Cullenia exarillata
(c) Sterculiaceae
The palynological data of the Sterculiaceae members studied reveal that
the family is highly eurypalynous with different apertural type such as 3colpate, 3-colporate, 4-5 colporate, 3-porate and 3-pororate. Out of the five
tribes investigated four of them are eurypalynous.
Eurypalynous tribes
Sterculieae
3-zonocolpate, 3-zonocolporate
Dombeyeae
3-zonoporate, 3-zonopororate
Hermannieae
3-zonocolporate. 4-5 -zonocolporate
Buttnerieae
3-zonocolpate, 3-zonocolporate
Stenoplynous tribe
Helictereae
3-zonoporate
In the case of eurypalynous tribes, further groupings at generic level may
be possible based on the aperture character, and the following groupings are
proposed in 4 tribes such as Sterculieae, Dombeyeae, Hermannieae and
Buttnerieae.
Tribe Sterculieae
Grains 3-zonocolpate
Firmiana
Grains 3-zonocolporate
Sterculia
Pterocyrnbium
Cola
Heritiera
Tribe Dombeyeae
Grains 3-zonoporate
Melhania
Grains 3-zonopororate
Dornbeya
Tribe Hermannieae
Grains 3-zonocolporate
Melochia
Grains 4-5-zonocolporate
Waltheria
Tribe Buttnerieae
Grians 3-zonocolpate
Theobroma
Leptonychia
Grains 3-zonocolporate
Guazuma
Different species within a genus were found to posses different pollen
morphoforms with respect to secondary and tertiary characters, and the
following groupings are proposed in them.
Sterculia
Grains 3-zonocolporate
Endocolpium circular
Endocolpium lalongate
Surface faintly reticulate
Shape subprolate
S.villosa
Shape spheroidal
S.urens
Surface reticulate
Shape subprolate
Endocolpium faint
Surface reticulate
Shape prolate spheroidal
S.campanulata
Shape prolate
S.balanghas
Firmiana
Grains 3-zonocolpate
Surface reticulate
Shape prolate
Pterocymbium
Grains 3-zonocolporate
Endocolpium lalongate
Surface reticulate
Shape prolate spheroidal
Cola
Grains 3-zonocolporate
Endocolpium circular
Surface foveolate
Shape prolate
C.acuminata
Heritiera
Grains 3-zonocolporate
Surface foveolate
Endocolpiurn faint
Shape prolate spheroidal
H.littoralis
Endocolpium circular
Shape oblate spheroidal
Tribe Helictereae
Kleinhovia
Grains 3-zonoporate
Pore circular
Surface foveolate
Shape oblate
H.papilio
Helicteres
Grains 3-zonoporate
Pore circular
Shape oblate
Surface papilate and finely granulate
Pterospermum
Grains 3-zonoporate
Pore circular
Shape spheroidal
Exine granulose and spinate
P.diversifolium
(Size dimorphism)
Surface foveolate
Pore larger
P.rubiginosum
Pore smaller
P.suberifolium
Tribe Dornbeyeae
Dombeya
Grains 3-zonopororate
Pore circular
Shape spheroidal
Surface granulose
Average size above 45pm
D.spectabilis
(Size dimorphism)
Average size below 35pm
D.calantha
Surface foveolate
Average size above 65pm
D.nehalensis
(Size dimorphism)
Melhania
Grains 3-zonoporate
Pore circular
Shape spheroidal
Surface granulose and spinate
M.incana
Tribe Hermannieae
Melochia
Grains 3-zonocolporate
Endocolpiurn lalongate
Shape oblate spheroidal
Surface reticulate
Average size above 30pm
M.indica
Surface foveolate
Average size below 30pm
M.nodiflora
Endocolpiurn circular
Shape prolate spheroidal
Surface foveolate
Average size below 20pm
Waltheria
Grains 4-5zonocolporate
Endocolpium lalongate
Surface reticulate
Shape oblate spheroidal
W. indica
Shape suboblate
W. americana
Tribe Buttnerieae
Guazuma
Grains 3-zonocolporate
Ora faint
Surface faintly reticulate
Shape prolate spheroidal
Theobroma
Grains 3-zonocolpate
Surface reticulate
Shape oblate spheroidal
T. cacoa
Leptonychia
Grains 3-zonocolpate
Surface reticulate
Shape oblate
Grains larger
L, caudata
Grains smaller
L.moacurroides
(d) Tiliaceae
Palynological data on the Tiliaceae reveal that the family is highly stenopalynous with
3- colporate apertural type.
Stenopalynous tribes
Brownlowieae
Berrya
3 - zonocolporate
Grewieae
Grewia
3 - zonocolporate
Triumfetta
3 - zonocolporate
C orchorus
3 - zonocolporate
Muntingia
3 - zonocolporate
Tilieae
Tribe Brownlowieae
Berrya
Grains 3-zonocolporate
Endocolpium lolongate
Surface foveolate
8. ammonilla
8.cordifolia
Grewia
Grains 3-zonocolporate
Endocolpium circular
Shape subprolate
Surface faintly reticulate
Shape prolate
Surface retipilate
Average size above 40pm
G.bracteata
Average size below 30pm
G.orientalis
G.serrulata
Surface reticulate
Average size above 30vm
G.darnine
Average size between 20-30vm
G.oppositifolia M II
G.disperrna
G.hetrotrichae
Average size below 20pm
G.tenax
G.nervosa M I
Endocolpium faint
Shape prolate
Surface reticulate
Endocolpiurn lalongate
Shape prolate
Surface reticulate
Average size above 25pm
G.oppositifolia M I
G.lanceaefolia
Average size below 25pm
G,tiliifolia
G. urnbellifera
Surface foveolate
G.nervosa M Ill
Triumfetta
Grains 3-zonocolporate
Endocolpiurn lalongate
Shape prolate
Surface faintly reticulate
T.pentandra
T.annua
Surface retipilate
T. pilosa
Trhomboidea
Tribe Tilieae
Corchorus
Grains 3-zonocolporate
Shape prolate
Endocolpium lalongate
Surface faintly reticulate
C. capsularis
C. olitorius
C. trilocularis.
C. aestuans M II
Endocolpium circular
C. aestuans M I
Muntingia
Grains 3-zonocolporate
Endocolpium lalongate
Surface foveolate
Shape sub prolate
Average size below 10pm
4. Morphological Evolution of Pollen Grains
Pollen grains, being the most vital unit in plants, evolution reflected in
their morphology is considered to be indicative of the course of evolution of
plant forms which they represent (Nair, 1970a). Apertural evolution of the
pollen is considered to be the most significant, which has been applied in
resolving the problems of plant taxonomy and phylogeny. Generally the
courses of morphological evolution of pollen are assessed based on the
position of the aperture, their number and form (Walker and Doyle, 1975; Van
Carnpo. 1976). Proximal, distal, zonal and global are considered to be the
hierarchical order of evolutionary progress (Nair, 1974a), of which the zonal
and global are restricted to the angiosperms. An evolutionary sequence from
simple to more complex apertural types has generally been contemplated
(Chanda et a/., 1979), and increase in the number from the primitive to
advanced appears to be the general trend. The pollen grains of monocots
have one aperture and those of dicots usually three. The inaperturate
condition occurs in the most primitive monocots and in the primitive dicots.
Wodehouse (1936) has investigated the phylogenetic changes in the germinal
furrow in relation to function. Apart from the monocolpate form, the trilete and
3-zonocolpate forms have been considered by him to be of basic significance
in apertural evolution, and major evolutionary changes in aperture have been
considered to have started from the one-furrowed forms of primitive
gymnosperms (Bennettitales and Cycadales) by the process of "modification,
protection or elimination of the wide open furrow ". According to Vishnumittre
(1964), the most primitive form is the trilete type from which has evolved the
inaperturate type followed by the aperturate ones.
Walker
(1974) has
considered the inaperturate pollen grains as the primitive, from which evolved
the aperturate ones, of which the tricolpate type is the progenitor of all the
other aperture forms in angiosperms. Nair (1965a, 1968, 1970c) who also
considered the aperture of pollen as of fundamental and conservative
importance, has proposed that the evolution of the dicotyledons itself has
taken place along two lines, one along the line of the Magnoliaceae and the
other along the line of the Rannunculaceae, represented by the fundamentally
monocolpate and the tricolpate forms respectively, while the monocots with
predominantly monocolpate morphoform evolved along an independent line.
The above propositions formed the basis of his triphyletic theory of origin and
evolution of the angiosperm (Nair, 1976).
In the evolutionary scheme of the Ranalian dicotyledons, the 3zonocolpate-pollen type is the fundamental one (Tewari and Nair, 1979). The
colporate, porate, pororate and spiraperturate are considered to have been
evolved from the colpate type by reduction and specialization of the apertures.
The change in form has also been accompanied by an increase in the number
of apertures. It has been generally accepted that pores are more advanced
than colpi, and pantoporate condition the most advanced one (Jonker, 1974).
The basic difference between monocots and dicots in pollen character is
concerned with the number and position of the aperture in the pollen grain
(Puri, 1990). In addition to the germinal aperture, there are also other
morphological characters in which evolutionary phenomena are expressed.
Walker and Doyle (1975) have suggested that the evolutionary trends in the
pollen wall architecture offer great potential as sources of polygenetic
informations of major importance. It is reported that the depression type and
excrescence types are parallel in evolution having diverged from the Psilate
(smooth) state as the one observed in the most primitive vascular plant
Rhynia (Eggart, 1974). In the Asteraceae, Wodehouse (1935) has observed a
gradual reduction in the exinous excrescences of the pollen grain. In the
Polygonaceae, pollen types with thick and heavily ornamented exine have
been considered to be the primitive, while those with thin, unornamented and
lightly ornamented exine as advanced (Wodehouse. 1931). Among the
cultivated varieties of Canna, Nair (1960) has traced a gradual reduction in
the exinous process followed by radial splitting of the exine producing free
columella.
Shape and size of pollen do not posses much phylogenetic significance
(Walker, 1976). Le Thomas (1980,1981) and Walker and Walker (1984) have
held the opinion that large boat - shaped, granular and monosculcate pollen is
the primitive type in angiosperms. With regard to the shape of pollen grains,
oblate grains are more advanced than prolate (Clarke, 1980)
Evolution of aperture
(A) Malvaceae
From the palynological data of the Malvaceae obtained in the present
study (77 species in 19 genera under 5 tribes) a brief consideration of the
morphological evolution of the pollen grains in the family has been made. It
was found that the family is eurypalynous with pantoporate, 6-porate,
pantocolporate. 3-colporate types. Out of the five tribes, 3 are stenopalynous
with pantoporate condition and the remaining two tribes possessing different
apertural types such as 3-zonocolporate, pantocolporate, 6-zonoporate and
Text fig. 17. Tentative scheme of evolution of pollen aperture in the
South Indian Malvaceae.
pantoporate. The distribution of various tribes which possesses the different
apertural type (according to the Nair's scheme of apertural evolution) is given
below.
Pantoporate
Decaschistieae
Hibisceae
Malvavisceae
6-zonoporatelpantocolporate
Gossypieae
Colporatel pantoporate
Malveae
According to this scheme (Text Fig. 17), the most primitive apertural
form in the Malvaceae occurs in the tribe Malveae from which evolution has
taken place to pantoporate which is seen in all the genera of the tribe except
Abutilon (3-colporate). The tribe Gossypieae appears to be more evolved with
one genus showing pantocolporate condition (Thespesia) and all the rest 6 zonoporate
(Gossypium). All the other three
tribes
(Decaschistieae,
Hibisceae, Malvavisceae) appear to be the most evolved in the family with all
the members being pantoporate.
(B) Bombacaceae
From the palynological data of the Bornbacaceae obtained in the
present study, a brief consideration of the morphological evolution of the
pollen grains in the family was made. It was found that the members of the
family are stenopalynous with colporate condition in two tribes, and one tribe
Text fig.18. Tentative scheme of evolution of pollen aperture in the
South Indian Bombacaceae.
eurypalynous with different apertural types such as colpate and colporate. The
distribution of various tribes which posseses the different apertural type (according
to the Nair's scheme of apertural evolution) is given below (Text Fig.18).
Colpate 1 colporate
Adansonieae
Colporate
Ceibeae
Durioneae
In the Bombacaceae, out of the three tribes studied, Adansonieae
possess the primitive 3-colpate grains in one species, and still more evolved
colporate in another species. In the other two tribes all the taxa studied had
colporate grains. The data is suggestive that Adansonieae is the least evolved
tribe in the Bombacaceae.
(C) STERCULIACEAE
The palynological data of the Sterculiaceae members studied reveal
that the family is highly eurypalynous with different apertural type such as 3colpate, 3-colporate, 4-5 colporate. 3-porate and 3-pororate. Out of the five
tribes investigated four of them are eurypalynous (Text Fig. 19).
EURYPALYNOUS TRIBES
3-zonocolpatel3-zonocolporate
Sterculieae
3-zonoporatel3-zonopororate
Dombeyeae
3-zonocolporatel4-5 -zonocolporate
Hermannieae
3-zonocolpatel3-zonocolporate
Buttnerieae
Text fig. 19. Tentative scheme of evolution of pollen aperture in the
South Indian Sterculiaceae.
STENOPLYNOUS TRIBE
3-zonoporate
Helictereae
Out of the five tribes, of the Sterculiaceae studied, two (Sterculieae,
Buttnerieae) had primitive 3-colpate grains in one and two genera respectively
and the rest with colporate grains. The tribe Hermannieae had grains with 3colporate, 4-5 colporate grains, while the tribe Helictereae showed 3zonoporate grains, and Dombeyeae 3-porate and 3-pororate grains. Apertural
situation in Sterculiaceae indicates that the tribe Buttnerieae and Sterculieae
are the most primitive, Hermannieae the intermediate and the other two
Helictereae and Dombeyeae, particularly the latter is the most evolved.
(D) TILIACEAE
Palynological data of the Tiliaceae reveals that the family is highly
stenopalynous with 3- colporate apertural type (Text Fig. 20).
STENOPALYNOUS TRIBES
3- zonocolporate
Brownlowieae
Grewieae
Tilieae
As far as the Tiliaceae is concerned all the members of the three tribes
(Brownlowieae, Grewieae, Tilieae) studied are relatively more evolved. They
have exclusively three zonocolporate grains.
Text fig. 20. Tentative scheme of evolution of pollen apertaure in the
South Indian Tiliaceae
5. SYSTEMATIC CONSIDERATION
The Malvales are a natural group characterized by the presence of
stellate, pubescent and mucilaginous cells or canals. The members are
predominantly woody plants of pantropical and subtropical distribution. The
stamens are usually many and united into a column and hence the group was
named columniferae by Eichler. Bessy (1915) assumed that Malvales have
originated from the Ranales via the Rosales. Halier has held that the Ranales
were the direct ancestor of Malvales through Bombacaceae. Others like
Rendle (1967) believed that the Guttiferales gave rise to the Malvales. The
Malvales forgoes a link with the Euphorbiaceae due to the frequent
occurrence of branched multicelluar hairs and ovary structure, which often
separates into one-seeded parts in the fruit. An endotropic course of the
pollen tube is common to both the groups. Members of the Thymelaeales are
considered to be closer to Tiliaceae, and, directly related to the ancestors of
the Malvales, which arose from the ancestors of the Flacourtiaceae type.
Malvales are considered to be closely related to the Cistales (Thorne,
1992; Takhtajan, 1997). Both of them have many common features with
Flacourtiaceae and Elaeocarpaceae as well as with the archaic members of
the Theales. Anatomy of the vegetative organs and palynological evidence
both confirm the origin of Malvales as well as the Cistrales from the
Flacourtiaceae through the intermediate group Scolopieae (Keating, 1972;
Miller, 1975). This is also confirmed by chernotaxonomical data. According to
the different taxonomists, positioning of the different families within the order
Malvales varies. Wettstein (1935) and Rendle (1967) have included the
families Tiliaceae, Bombacaceae, Sterculiaceae and Malvaceae in this order.
According to Engler and Prantl (Vasishta 1990), the Malvales have four sub
orders, of which the suborder Malvineae include the four families Tiliaceae,
Malvaceae, Bombacaceae and Sterculiaceae. Gunderson (1950) has followed
the Englerian concept with reference to the order. Bessy expanded the order
incorporating into it the Balanopsidaceae, Ulmaceae, Moraceae and Urticaceae.
Lawrence (1951) has treated the Malvales, as containing five families.
Elaeocarpaceae, Tiliaceae, Malvaceae, Sterculiaceae and Bombacaceae.
Bentham and Hooker (1865) have included three families in his order
Malvales (Malvaceae, Sterculiaceae and Tiliaceae) of which the Tiliaceae
include Elaeocarpaceae, and Bombacaceae in the Malvaceae. According to
Hutchinson's treatment (1959), the Malvales include only the Malvaceae, the
other three families (Tiliaceae, Bornbacaceae, and Sterculiaceae) being
treated under his new order the Tiliales. He has considered the Malvales to be
more advanced than Tiliales. In the Dahlgren's (1980) system, the Malvales
are a much larger assemblage with 12 families (Bixaceae, Bombacaceae,
Cistaceae, Cochlosperrnaceae, Dipterocarpaceae, Huaceae, Malvaceae,
Plagiopteraceae, Sterculiaceae, Sphaerosepalaceae. Sarcolaenaceae and
Tiliaceae), while Goldberg (1986) and Cronquist (1988) have both included
Bombacaceae, Elaeocarpaceae, Malvaceae, Sterculiaceae and Tiliaceae in
their Malvales. Thorne (1992) defines the order to include the Bixales,
Cistales and the Thymelaeales, while Takhtajan (1997) has put the
Thymelaeales in his Euphorbianae, retaining the Cistales (including the
Bixales) within his Malvanae. Reveal (1997) restricted the Malvales to
accommodate
six
families
(Tiliaceae,
Dirachmaceae,
Byttneriaceae,
Sterculiaceae, Bombacaceae and Malvaceae). Thorne (2000), in his latest
classification divided the core Malvales into 3 families such as the (1)
expanded Malvaceae, (2) Bombacaceae, and (3) the reduced Tiliaceae, and
Byttneriaceae. The order Malvales corresponds to the 4 traditional families
Malvaceae, Bombacaceae, Sterculiaceae and Tiliaceae (APG, 1998). There
is no dispute that they form a natural grouping - the "core Malvales".
Muntingia and Discraspida have in the past been associated with Tiliaceae,
which are now classified in a separate family Muntingiaceae (Bayer et a/.,
1999; Alverson et a/., 1999). However,, Judd and Manchester (1997) have
suggested that the Malvaceae. Sterculiaceae and Bombacaceae are
monophyletic. Alverson et a/. (1998), suggests that the malvalian complex is
composed of four groups (1) the four core families, Bombacaceae,
Malvaceae, Sterculiaceae, Tiliaceae; (2) the bixoid families, Bixaceae.
Cochlospermaceae and Sphaerosepalaceae; (3) the thymelaealan family,
Thymelaeaceae; and (4) the cistalan families, Cistaceae. Dipterocarpaceae,
Sarcolaenaceae and the newly proposed Muntingiaceae.
The family Malvaceae is included under the order Malvales by most of
the leading taxonomists like Bentham and Hooker (1865); Hutchinson (1959);
Engler (1964); Rendle (1967); Dahlgren (1980); Takhtajan (1980); Cronquist
(1981); Thorne (1992); Takhtajan (1997); Reveal (1997); Thorne (2000) and
Bayer and Kubitzki (2002). Kearney (1951) have recognized five tribes in the
family such as Malopeae, Hibisceae, Malveae, Abutileae and Ureneae.
Hutchinson
(1959) supported
Kearney's
classification. According
to
Schumann (1890) the family Malvaceae has four tribes such as Malopeae,
Malveae, Ureneae and Hibisceae. Fryxellii (1973) has described the
Malvaceae into five tribes Malveae, Gossypieae, Hibisceae, Malvaviscus and
Decaschistieae.
Bentham and Hooker (1862) distinguished four tribes in his Malvaceae
viz, Malveae, Ureneae, Hibisceae and Bombaceae based mainly on the
nature of the stamina1 column, the relative number of styles and carpels and
the nature of fruits. He distinguished four sub tribes (Malopeae, Eumalveae,
Sideae and Abutileae) under the tribe Malveae based on the number of
carpels, number of ovules per carpel and the nature of stigmas. Masters
(1874) has followed Bentham and Hooker, and recognized four tribes in this
family in India, but he did not recognize any sub tribes under the tribe
Malveae. Since Masters (1874), the tribe Bombaceae has been treated as a
separate family based mainly on its free or shortly connate stamens, two or
many thecous anthers and smooth pollen grains.
The delimitation of the family Bombacaceae based on macro
morphological characters and its separation from the closely related families
(Sterculiaceae, Malvaceae and Tiliaceae) seems to be rather a matter of
convenience. The Bombacaceae has been treated as a separate family and
included it in the order Malvales by many taxonomists like Engler (1964);
Takhtajan (1980); Dahlgren (1980); Cronquist (1981) and Thorne (1992) while
Hutchinson (1959) included it in his order Tiliales. Bentham and Hooker
(1865) who have not recognized this as a separate family have included it
under the family Malvaceae. Palynomorphological characteristics were used
as additional criteria for a better delimitation of the family Bombacaceae. This
has been confirmed on palynological ground by Erdtman (1952). A great deal
of subsequent work has been done, mainly by Tsukada (1964); Fuchs (1967)
and Robyns (1971).
The Bombacaceae, as a family
includes six tribes
(Durioneae, Hampeae, Matisieae, Catostemmateae, Adansoniaceae and
Ceibeae) and is represented in India by three genera (Bombax, Ceiba,
Cullenia), and in addition there are a few other exotic ones as Adansonia,
Durio and Ochroma.
The Bombacaceae has been considered to be clearly related to the
Malvaceae and Sterculiaceae and in the past their members were frequently
included in the former from which it is distinguished by the smooth pollen
grains, and the pericarp of the fruit, i.e., pithy to woolly. Staminodes are more
common in this family in comparison to Malvaceae and Sterculiaceae. These
three families are difficult to differentiate from one another and yet the vast
majority is easily placed, especially when observed in the field. As noted by
Mabberley (1997) Nowicke and Baum (2000), several genera have moved
among the three families without really settling convincingly into any one. The
problem of generic replacement is manifested in the difficulties encountered in
the evidence presented by Judd and Manchester (1997) for combining
Sterculiaceae and Bombacaceae into the Malvaceae. In a broad sense, and
as now generally defined, these families cannot be distinguished.
Cronquist (1988) has separated the Bombacaceae from the Malvaceae
in view of certain fine and technical differences like generally smooth or
merely rugose, triaperturate pollen grains versus minutely spiny, pantoporate
grains. He considers that the larger tree habit is diagnostic enough to
distinguish Bornbacaceae from the herbaceous to shrubby or occasionally
small-treed Malvaceae. Takhtajan's (1997) conclusion that the Bombacaceae
may be distinguished from the Sterculiaceae by their "bisporangiate and
unilocular anthers and flowers, which often are subtended by an epicalyx."
Sterculiaceae stands close to both the Tiliacae and the Bombacaceae
and Malvaceae. The boundaries between and among these families are very
clear. The taxonomic position of some genera especially the paleaotropical
genus Leptonychia with the strongly buillate seeds having fibrous exotegmen
is neither Sterculiaceous nor Tiliaceaous (Corner, 1976). Sterculiaceae are
very near to Tiliaceae, a view confirmed by the anatomy of vascular system of
the petiole. But the family Sterculiaceae is very divers and is characterized by
a great diversity of morphological, anatomical and palynological features. In
particular there are so many differences between the Buttnerioideae and
Sterculioideae that Edlin (1935) proposed to accept them as two separate
families on account of the difference in the structure of their wood, vegetative
organs, flowers, and fruit. However, the boundary between these two groups
is not so very clear-cut. For example on the basis of the vascular system of
the petiole, the tribe Buttnerieae is considered closer to the Sterculiaceae
than to the other tribes of the Buttnerioideae (Gazet du chatelier, 1940 a, b).
Besides, as Rao (1952) has shown, the structure of the androecium is similar
for the whole family and therefore there is no reason to separate the
Sterculioideae in a family of their own.
The Sterculiaceae are divided into two subfamilies by Thorne (1992),
Sterculioideae and the Dombeyoideae. The latter has long been considered
as a distinct family Buttneriaceae (Whitlock et al., 2001). Takhtajan (1997)
has accepted the same two subfamilies, but further subdivided these into a
series of tribes. Edlin (1935) has suggested that Byttneriaceae should be
taken up as a distinct family.
Takhtajan (1997) and Thorne (2000) have divided the Tiliaceae into
three subfamilies: Tilioideae, Brownlowioideae and Neotessmannioideae.
Both of them have kept Muntingia in the tribe Tileae. The definition of
Tiliaceae has remained consistent while various genera have moved in and
out of the family, the core genera being Grewia, Triumfetta and Tilia. The
family's close relationship to Malvaceae has also been long recognized,
although Hutchinson did refer Tiliaceae to the Tiliales based on his
fundamental assumption that there was a major evolutionary division between
plants that are primarily herbaceous and those that are primarily woody
(Hutchinson. 1959). Bremer and Thulin (1998) consider the Tiliaceae to be
gynonyrnous with Malvaceae.
The Tiliaceae has been dealt with differently by different taxonomist.
Bentham and Hooker (1 862) have included the members of Elaeocarpaceae
in the Tiliaceae, whereas, Schumann (1890) assigned an independent family
status to the Elaeocarpaceae. Muntingia is treated under the Elacocarpaceae,
whereas Bentham and Hooker described it under Tiliaceae, in the Tribe
Tilieae. Hutchinson (1959) has placed Elacocarpaceae under Tiliaceae.
Colpate condition has been considered to be primitive character, while the
colporate and porate conditions and larger number of apertures, etc., as
advanced. According to the concept the family Tiliaceae is to be considered
comparatively advanced on morphological ground as its members mostly
possess colporate pollen grains.
Of the various classificatory treatments of the Malvales, Bentham and
Hooker's classification is the most comprehensive of the classical ones and
Hutchinson's and Takhtajan's of the modern. As already pointed out, there
exists several areas of disagreements between and among these three
classifications concerning the treatment of the order Malvales. The notable
disputed relationships pertaining to the genera and tribes included in the
present study are briefly considered in the light of available palynologcal data
with special reference to the information on the South Indian group reported in
the study. Table. 18 and 19 shows the palynologically known genera and
tribes arranged according to the system of Bentham and Hooker (1865),
Hutchinson (1959) and Takhtajan (1996). The major aspects of deviation and
similarity between and among the three treatments are highlighted as under:
Table 18. Comparison o f different systems of classification of family Malvaceae and Bombacaceae
Bentham and Hooker-1865
Pollen aperture
Exine sculpturing
Hutchinson - 1959
Family Maivaceae
Family Malvaceae
Takhtajan -1996
Family Malvaceae
Tribe Malveae
Tribe Hibisceae
Subtribe Eumalveae
Althea
Pantoporate
Lavatera
Pantoporate
Malva
Pantoporate
Malvastrum
Pantoporate
Granulosq
~ranulosel
,
I I
[Decaschistia
Decaschistia
Hisiscus
Abelmoschus
Abelmoschus
Kydia
Sub Tribe Sideae
Sida
Tribe Hibisceae
Gossypium
Pantoporate
Sub tribe Abutilieae
Thespesia
Tribe Malveae
Tribe Malveae
Sub tribe Malvinae
Malva
Kydia
Pantoporate
Abutilon
3-zonocolporate
Aithea
Modiola
Pantoporate
Lavatera
Tribe Ureneae
Malachra
Tribe Abutilieae
Pantoporate
Tribe Abutilieae
Abotilon
Pantoporate
Sub tribe Abutilinae
Sida
Pavonia
Pantoporate
~ranulosel
Abutilon
Malvasrrum
Malvaviscus
Pantoporate
Granulose
Modiola
Tribe Ureneae
Sub tribe Sidinae
Malvaviscus
Sida
Malchara
Tribe Hibisceae
Decaschistia
Pantoporate
Granulose
Hibiscus
Pantoporate
Granulose
Thespesia
Pantocolporate
Granulose
Gossypium
6 zonoporate
Granulose
1
t
L Malvastrum
Tribe Ureneae
Urena
Pavonia
Urena
Tribe Bombaceae
Family Bombacaceae
Family Bombacaceae
Sub tribe Adansonieae
Tribe Durioneae
Tribe Durioneae
Bombax
3 colpatel colporate
Reticulate
Cullenia
Cullenia
Eriodendron (Ceiba)
3 colporate
Reticulate
Tribe Adansonieae
Tribe Bombaceae
ombax
I I
Sub tribe Durioneae
Cullenia
3 colporate
1
Foveolate
Tribe Ceibeae
LCeiba
Bombax
Tribe Ceibeae
Ceiba
Table 19. Comparison of different systems of classification of family Sterculiaceae and Tiliaceae
Bentham and Hooker-1865
Pollen aperture
Exine sculpturing
Family Sterculiaceae
Hutchinson - 1959
Takhtajan -1 996
Family Sterculiaceae
Family Sterculiaceae
-
Tribe Dombeyeae
Tribe Sterculieae
Tribe Byttnerioideae
Sterculia
3 zonocolporate
Reticulate1
~Dombeya
Finniana
3 zonocolpate
Reticulate-.
Melhania
Melochia
Pterocymbium
3 zonocolporate
Reticulate
Tribe Hermannieae
Waltheria
Cola
3 zonocolporate
~oveolate-1
Sub Tribe Hermannieae
Sub tribe
Theobromaeae
Hentiera
3 zonocolporate
Foveolat
Leptonychia
Tribe Theobromeae
Tribe Helictereae
Theobroma
Kleinhovia
3 zonoporate
Guazuma
Helicteres
3 zonoporate
Sub Tribe Helictereae
Pterospermuin
3 zonoporate
Pterospermurn
Tribe Dombeyeae
Dombeya
3 zonopororate
Melhania
3 zonoporate
Triha Unrmc,nnin=a
Granulose
Kleinhovia
-,
Sub Tribe Dornbeyeae
Dombeya
Triha S t o r r ~ ~ l i o a a
Molhnnin
Waltheria
4-5
~ e t i c u l a t e - 7 L U cFirrniana
Sub Tribe Sterculieae
zonocolporate
Tribe Buttnerieae
Theobroma
3 zonocolpate
Reticulate+
Guazuma
3 zonocolporate
R e t ~ c u l a tI e
I- cola
Tribe Tarrietieae
Firmtana
Pterocymbium
Cola
Sub Tribe Tarrietieae
Heritiera
Family Tiliaceae
I
Tribe Brownlowieae
Berrya
3 zonocolporate
Foveolate
Family Tiliaceae
Family Tiliaceae
Tribe Enfeleeae
Tribe Tilioideae
Sub Tribe Corchoreae
Tribe Grewieae
Grewia
3 zonocolporate
Triumfetta
3 zonocolporate
Reticulate
Tribe Tilieae
Corchorus
Sub Tribe Tilieae
Muntingia
Tribe Tilieae
Corchorus
3 zonocolporate
Reticulate
Muntingia
3 zonocolporate
Foveolate
Tribe Triurnfetteae
Grew~a
Leptonychia
3 zonocolpate
Reticulate
Tnurnfeita
Sub Tribe Triurnfetteae
Sub Tribe Grewieae
L
Tribe Berryeae
Triumfetta
Berrya
Tribe Brownlowieae
Sub Tribe Berryeae
Berrya
Bentham and Hooker (1865) have included the Malvaceae in his
Malvales along with Sterculiaceae and Tiliaceae. Hutchinson's Malvales
comprises only a single family, the Malvaceae. He has included Tiliaceae,
sterculiaceae and Bombacaceae under a different order, the Tiliales along
with three other families (Schisopetalae, Perediscaceae and Diarchmaceae).
According to Taktajan's classification the order include the Bixales and
Cistales. It may be noted that in the Bentharn and Hooker's treatment there is
no separate family status for Bombacaceae (instead the taxa are considered
under a tribe Bombaceae).
The tribe Malveae has been treated variously by different taxonomists.
Bentham and Hooker have divided it into several sub tribes of which
eumalveae includes Althea, Lavatera, Malva and Malvastrum, sub tribe
Sideae includes Sida and the sub tribe Abutilieae includes Kydia, Abutilon and
Modiola. Hutchinson has separated the Malvastrum from eumalvae sub tribe
and placed it under sub tribe Sidieae in the tribe Abutilieae. Takthajan has
taken out the Malvastrum from Bentham and Hooker's eurnalveae and placed
under the tribe Abutilieae along with Abutilon and Sida. Palynologically
Malvastrum possess different exine pattern (foveolate) from that of other
members of eumalveae (granulose). Thus the separation of Malvastrum from
the rest of eumalvae is justifiable. Based on the palynological characters of
Sida (pantoporate), the status given to it by Takhtajan along with Abutilon (3
zono colporate) in the tribe Abutilieae is not supported, while the other's
treatment of Sida (with a separate sub tribal status) is more relevant. The
Tribe Hibisceae includes Decaschistia, Hibiscus, Jhespesia and Gossypium
as proposed by Bentham and Hooker. Hutchinson and Takhtajan have
effected
considerable
modification by
realigning
some
genera
like
Abelmoschus and Kydia, whereas Bentham and Hooker included Kydia under
his Sub tribe Abutileae. Based on the primary palynological character
(pantoporate condition as in the case o f V q j o i i $ j ophibiseae members)
shifting of Kydia from Abutiliae (3zonocolporate) and its placement under
Hibisceae appears to be relevant. Takhtajan and Hutchinson treated the tribe
Ureneae of Bentham and Hooker by and large in a similar way. The family
Bombacaceae (Hutchinson and Takhtajan) was treated as a tribe,
Bombaceae by Bentham and Hooker. Cullenia is treated in the same way by
all the three classificatory systems. The tribe Durioneae (Hutchinson and
Takhtajan), in Bentham and Hooker's system occupies a sub tribal status.
Bombax and Ceiba have been included under the sub tribe Adansonieae by
Bentham and Hooker, but Hutchinson retained Bombax in the tribe
Adansonieae, while Takhtajan placed it under the tribe, Bombaceae; and
Ceiba has been given a tribal status Ceibeae by both Hutchinson and
Takhtajan.
Not much variation is observed among the three classificatory systems
in the position of the tribe of the Sterculiaceae except the two sub families
(Byttneriodieae and Sti2rculioideae) proposed by Takhtajan. Hutchinson and
Takhtajan have kept most of Bentham and Hooker's genera of Sterculieae
except Heritiera, which has been elevated to a tribe. Tarrietieae. Both
aperture and exine patterns of the members of Sterculieae studied were much
common (3 colporate and reticulate pattern) with Heritieria, and thus the
separate tribal status of Heritieria is not much relevant on the palynological
basis. The tribes Helictereae, Hermannieae and Dombeyeae are treated by
and large similarly in all the three classificatory systems. Bentham and Hooker
placed Theobroma and Guazuma under the tribe Buttnerieae, but both the
others treated it under the tribe, Theobromeae along with Leptonychia.
Bentham and Hooker have put Grewia and Triumfetta together under
his tribe, Grewieae, but the others (Hutchinson and Takhtajan) treated them
under two different tribes Grewieae and Triumfettae. Considering the primary
palynological feature, the species of Triumfetta studied here had only
lalongate ora, while species of Grewia possess both circular and lalongate ora
and hence the separation of Triumfetta from Grewieae and elevating it to a
separate tribe, Triurnfettae is justifiable. Bentham and Hooker's Tilieae
includes Corchorus, Muntingia and Leptonychia, Hutchinson and Takhtajan
have removed Leptonychia from the Tiliaceae, and placed it under the
Sterculiaceae in the tribe, Theobromeae; and this interfamily change
apparently gains support from the present palynological evidence due to the
presence of primitive three colpate grains in Leptonychia, whereas all other
members of Tiliaceae studied had advanced 3 colporate grains. Muntingia is
retained in the same tribe, Tilieae in all the three classificatory systems, while
Corchorus is shifted to a new tribe, Enteleeae by Hutchinson, and Corchoreae
by Takhtajan. Muntingia possesses very minute pollen grains with foveolate
exine pattern compared to the Corchorus where the grains are large and
reticulate. The separation of Corchorus from Tilieae is palynologically
justifiable on grounds of secondary and tertiary characters. Berrya has been
given a generic status by Bentham and Hooker under his tribe Brownlowieae,
while Hutchinson and Takhtajan have given it a separate tribal status
Berryeae.
The Bombacaceae has been treated as a separate family in both
Hutchinson's and Takhtajan's classification, while Bentham and Hooker have
given it only a tribal status under their Malvaceae (Bombaceae). Pollen
morphological data show that members of Bentham and Hooker's tribe
Bombaceae are clearly distinct from the rest of the entire Malvaceae as
regards both primary (colporate) and secondary (reticulate) exine pollen
features against the pantoporate and spiny pollen of the Malvaceae proper.
Palynological evidence provides amble support for the separate family status
for this group (Bombacaceae).
Regarding the placement of the genus Kydia, there is disagreement
between Bentham and Hooker and the other two (Hutchinson and Takhtajan).
In the formers system Kydia has been placed in their sub tribe Abutilieae,
while the latter two have kept this genus in their tribe Hibisceae. Kydia which
has pantoporate grains is distinct from the rest of Bentham and Hooker's
Abutilieae (3-colporate), and hence the placement of the genus to Hibisceae,
members of which are pantoporate, is appropriate.
Hutchinson and Takhtajan have both assigned the genus Ceiba a tribal
status in their family Bombacaceae. But Bentham and Hooker have treated
this as a genus in their tribe Bombaceae. Palynological evidence (colporate
aperture, reticulate exine similar to Bombax) does not seem to justify a
separate tribal status for Ceiba.
In all the three treatments, the genus Abutilon is kept as a genus in
their tribe Abutilieae. The present palynological information shows that
Abutilon, with colporate pollen grains, is distinct from the rest of the genera of
the tribe Abutiliae, and hence a separate monotypic tribal status for Abutilon
merits consideration.
In Bentham and Hooker's classification the genus Leptonychia has
been treated under the tribe Tilieae (Tiliaceae) along with Corchorus and
Muntingia. But Hutchinson and Takhtajan have shifted Leptonychia from the
tribe Tilieae and kept it under the tribe Theobromeae of their Sterculiaceae.
'The entire Tiliaceae have colporate pollen grains except Leptonychia
(colpate). 'This distinction apparently justifies its displacement from the
Tiliaceae and the
placement in the
Sterculiaceaei under the tribe
Theobromeae whose members are predominately colpate, and hence from
the palynological perspective, Hutchinson's and Takhtajan's treatment of their
genus appears to be appropriate.
The genus Muntingia has been treated on the same lines in all three
classifications under the tribe Tilieae. In terms of the aperture feature (3
colporate) their treatment appears to be appropriate. But in the recent
classification the genus Muntir~giahas been given a separate family status,
Muntingiaceae based on evidence from DNA and rbcL studies (Bayer et a/.,
1998; Bayer, 2002). One possible palynological support that can be construed
is the very minute size of pollen grains of species of Muntingia (6-9pm) so
distinct from the other members of Tiliaceae.