5. DISCUSSION
Biosystematical studies of 24 taxa of Euphorbiaceae have been
made with special reference to mitosis, meiosis, palynology, leaf anatomy
and epidermal characters. All these evidence have been undertaken to
understand the interrelationship among the species.
5.1. Chromosome number
Of the 24 taxa studied, first record of chromosome number have
been made in 1) Phyllanthus myrtifolius 2) Sauropus androgynus 3)
Aporosa lindleyana 4) Baccaurea courtallensis 5) Croton variegatum 6)
Croton sparsiflorus 7) Acalypha fruticosa 8) Jatropha glandulifera.
Deviant record of chromosome number as against the previous reports
has been made in 1) Chrozophora rottleri and 2) Excoecaria agallocha. In
the rest of the species studied the present report of chromosome
numbers confirm the earlier record of chromosomes numbers.
A common survey of the chromosome number in Euphorbiaceae
reveals the existence of graded series of haploid numbers, namely 6, 7, 9,
10, 11, 12, 13, 14, 15, 16, 17, 18, 20, 21, 22, 24, 26, 28, 30, 36, 50, 72,
100 and 112 (the so called Carex type and Antirrhinum type of Tischler
(1937), suggesting an increase by a few chromosomes or by one
chromosomes). Of those haploid numbers, n=10 and n=11 represented
the highest frequency among the taxa so far investigated in the family
and in his present investigation the taxa showed the same haploid
numbers, n=10 and n=11, representing the highest frequency (Figure-8).
Thus, of the 24 species a maximum of 5 species possesses 10 as the
haploid numbers (Figure-8) and the maximum of 4 species possesses 11
as the haploid number (Figure-8). It is logical to assume the original
primary basic number to be 10 which should have given rise to the
derived primary basic number, that is 11. In Euphorbiaceae, the highest
frequency to haploid chromosome numbers, that is, 10 and 11 are nearly
equal (Fedorov, 1974). So it may be inferred to that 10 may be the
original primary basic number and 11 the derived primary basic number.
This fact would perhaps appear to suggest that the haploid number 10
may be considered as the original primary basic number of this family,
from which the other haploid numbers, high and low might have been
derived.
Increase or decrease in chromosome numbers may be brought
about by various karyomorphology mechanisms. It has been suggested
that increase in the chromatin content, as by misdivision of the
centromere whereby unpaired chromosomes at the first meiotic division
break across into two halves which go to opposite poles, each arm
forming a new independent chromosome with a terminal kinetochore
(Darlington, 1939; Darlington and La Cour, 1950; Darlington, 1956); but
this has been observed only under experimental conditions (Mehra and
singh, 1968 and Natarajan and Upadhya, 1964). A more frequent method
of increase appears to be through polyploidy by longitudinal division and
unequal apportionment of the chromosomal halves between the daughter
cells. Aneuploid increase of
chromosome number may also be due to
non-disjunction of chromosomes of bivalents during first meiotic
division, so that one of the gametes come to bear an extra chromosome
and has a greater chance of survival than the gamete with one
chromosome less. If the gamete with an extra chromosome unites with a
normal gametes, the resulting plant is a trisomic (2n+1); or if it unites
with another gametes with an extra chromosome it becomes a tetrasomic
(2n+2). In either case, increase in chromosome numbers are generally
and more easily assimilated by the plant than decreases, which may lead
to environment, nutritional and even other disorders. Mechanisms are
known, however, by which decrease in chromosomes number may also
arise. A common method of chromosome decrease in by unequal
translocation between chromosomes (Stebbins, 1950); this has been
recorded in the genus Crepis, in which the main course of chromosomal
change is a progressive decrease in basic number from 6 to 3. Thus, a
decrease from n=4 in Crepis Neglecta or some related species to n=3 in
C. fuliginosa appears to have arisen through an unequal segmental
interchange, so that one chromosome of C. Neglecta (or a concerned
ancestor) lost nearly all its long arm. The chromatin attached to the
remaining centromere and the centromere itself are not found in
C. fuliginosa and have supposedly been lost (Togby, 1943; Babcock,
1947a). A similar derivation of C. kotschyana (n=4) from C. foertida (n=5)
has been explained by Sherman, (1946) and other examples in the
Cichorieae of Compositeae are given by Stebbins et al., (1953). In the
present study, in the family Euphorbiacee, a similar process of
chromosomal reduction might have been in operation so that a basic
number of n=10 might have got reduced to n=9, n=7 and finally to n=6
by a series of unequal translocations involving concurrent loss of inert
heterochromatin parts of the chromosomes. The haploid numbers, 6, 7
and 9 represent secondary basic numbers from which haploid numbers
might have derived through aneuploidy or euploidy. This view is
evidenced by statement of Heywood, (1967) that in the plant kingdom
even 14 may be considered as a polyploid number in as much as that the
herbaceous dicotyledons have been reported to show frequency curves of
n=7, 8 and 9. The evolutionary relationships to chromosome numbers of
the various species of Euphorbiaceae may be schematically represented
in the following diagram (Figure-9).
5.2. Chromosome size
As revealed by karyotype analysis of 24 species of Euphorbiaceae,
in the present investigation, there exists a close correlation between the
size and number of somatic chromosomes. For instance, the diploid
species of Euphorbia namely E. hitra has fewer number of somatic
chromosomes (2n=20). But at the same time, the chromosomes are
comparatively large in size (size range 3.0µm to 4.0µm). The species of
E. splendens possess more number of somatic chromosome (2n=40). But
at the same time, the chromosomes are comparatively smaller in size
(size range from 1.2µm to 2.4µm). In other words, the more number of
chromosomes the smaller is the size of the chromosome in E. splendens.
So also the size range of the somatic chromosomes of the diploid species
of Hevea brasiliensis (ranging from 1.8µm to 5.5µm) is the maximum size
range observed in this study. The same phenomenon may be visualized
in other species of Euphorbiaceae studied. Therefore, there is a close
correlation between the size and number of somatic chromosomes among
the species of Euphorbiaceae studied.
Sharma
(1978),
in
his
“Change
in
chromosome
concept”
-Dynamisms in change of chromosome size”, stresses the various points
regarding the nature of chromosomes. Different views exists about the
phylogenetic increase or decrease of DNA as well as chromosome size in
various biological systems (Stebbins (1971); Bachman et al., (1972); Rees
(1972); Sharma (1972); Sparrow and Naumann (1974); Bennett and
Smith (1976); Jones and Brown (1976); Narayan and Rees (1976); Price
(1976) and Szarski (1976). In polyploids, there has been a phylogenetic
reduction in chromosome size in a majority of cases (Darlington, 1956
and Sharma, 1974). Different theories have been proposed to account for
this decrease in chromosome size (Bennett and Rees, 1967). Later, in a
series of investigation on different species of plants including Vicia,
Commelina, Lens, Lathyrus, Ophiopogon and Nigella (Sharma, 1972) such
diminution in chromosome size from diploids to polyploids was obtained,
including even a sudden change in induced tetraploids in C1 generation
following colchicines treatment. The latter behavior indicates the
immediate response of chromosomes, in changing their pattern to meet
the needs of the altered set up. Heterochromatin has been shown to play
an
active
role
in
the
alternation
of
chromosome
size
through
condensation and deconsendation. Species with high heterochromatin at
the diploid level show such reduction in size, in polyploids. La Cour
(1951), noted a similar reduction on heterochromatic segments in
tetraploids of Trillium tschouoskii (cf. Takehisa, 1976). This reduction is
evidently an index of high degree of compaction or inactivity of the
segments which otherwise remained active at the diploid level and
conferred adaptability. The increase in gene dosage following polyploidy,
which itself confers adaptability, sets in motion the dynamic property of
chromosomes to segments to induce condensation and inactivity of
segments which become genetically redundant.
5.3. Karyomorphology
From the beginning of 20th century karyology has found a new
spheres of usefulness as an ally of taxonomy. In the recent period, quite
a large amount of literature has accumulated on his line of research
(Ehrendorfer, 1964 and Moore 1968). Karyomorphology, therefore, offers
much scope for the assessment of interrelationship among the various
species. In many cases, karyotype analyses have helped in the fuller
appreciation of taxonomic relationship within large groups of plants
resulting in a complete realignment of the classification of those groups
(Avdulov, 1931 and Gregory, 1941). In knowing such chromosome
studies, certain principles are usually in mind.
a) Polyploids are derived from diploids
b) Small chromosomes are usually found in taxa which may be
considered as derived from those with larger chromosomes.
c) Karyotype having metacentric chromosomes may be found in less
advanced plants than those in which there are telocentric
chromosomes of unequal size.
d) Original primary basic numbers give rise to derived primary basic
numbers and one or both are precursors of secondary basic
numbers.
e) There is always, in nature, reduction the basic number must
involve loss of a centromere and at least a small amount of
adjacent chromosomal material, while increase must involve at
first a duplicate chromosomes or centromere bearing fragment.
Implementation of such methods has been made by various
workers like Love and Love (1944) in boreal plants, Babcock (1947) in
Crepis, Goodspeed (1954) in Nicotiana, Sato (1943) in Liliaceae, Stebbins
et al., (1953) in Cichorieae, Sharma and Sakar (1956) in Palm,
Heimburger (1959) in Anemone, Kurita (1958) in Ranunculaceae,
Chennaveeraiah (1960) in Aegilops, Elumalai and Selvaraj (2013) in
Euphorbiaceae and a large number of others. Davis and Heywood (1963)
have fully discussed the cytotaxonomical aspects.
The concept of the karyotype analysis has been reviewed by many
authors in the recent past. (Stebbins (1950); Swanson (1957) and
Sharma and Sharma, 1959). Levitzky (1931) has shown that in the
primitive tribe, Helleboreae, reduction in chromosomes size of the entire
same complement has effected speciation in different degrees. He
delineated the evolution of the karyotype through a series of gradual
change in external appearance of the chromosomes. The genus
Helleborus contains a primitive complement having large isobrachial
chromosomes in low number. From such type, various specialized type
have been derived. The “V” shaped chromosomes alter first to “J” shape
and to the headed types with Sub-terminal centromeres. Secondary
specialization consists of reduction
in size of some chromosomes in
relation to others of the same chromosomes in relation to others of the
same set so that the socialized karyotypes contain the chromosomes of
very unequal size. These general tendencies have been recorded in
various genera and tribes of Angiosperms, eg. in Lathyrus (Senn, 1938),
in Crepis (Babcock, 1947), in Cichorieae (Stebbins et al., 1953), in
Eupatorium (Huziwara, 1956) and many others. Babcock et al., (1937)
found that primitive species of Crepidinae have many chromosomes
nearly equal in size with median centromeres and that with advancing
evolution, the chromosomes become unequal in size with sub-terminal
centromeres. Babcock summarizes the karyotype changes in Crepis,
under a number of distinctive heads, i.e., a progressive decrease in the
basic chromosome number, polyploidy and increase in asymmetry
(asymmetry in the sense, chromosomes with unequal arms) and a
decrease in chromosome size. The chromosome asymmetry in Crepis is
due to the consequence of unequal reciprocal translocations. Different
factors may be responsible for the reduction in the chromosome size and
gene mutations may furnish the basis for the trend in decreasing
chromosome size.
In the present study, critical karyotype analysis of as many as 24
species of Euphorbiaceae have been made. Of these, almost all the taxa
studied showed asymmetrical karyotype. It is one of the advanced
characters. Excepting Euphorbia splendens and Chrozophora rottleri, all
other genera studied here showed typical asymmetry in karyotypes. It is
a fact that the family belongs to the advanced category and is further
evidenced by their Shortest chromosome/Longest chromosome ratios,
Short arm/Long arm ratios, their relative lengths and also by the
common occurrence of sub-terminal kinetochores. This family, therefore,
may be considered as one of the most evolved families of Angiosperms.
5.4. Mitotic and Meiotic abnormalities
Precocious movement of chromosomes have been observed in
Jatropha curcas during mitotic division and in Jatropha multifida and
Acalypha indica during meiotic divisions. Due to these abnormalities, two
daughter cells with unequal chromatins in mitosis and 4 daughter cells
with unequal chromatins in meiosis will be formed, thus leading
ultimately to aneuploidy.
Due to the presence of aneuploid chromosome numbers in some of
the
species
of
Euphorbiaceae
studied,
univalents,
trivalents,
quadrivalents and multivalents are formed together with bivalents. The
separation of trivalents, quatrivalents and multivalents into univalents
during metaphase and early anaphase is abnormal. Due to this, the first
and second divisions of meiosis are unequal and 4 gamets with unequal
number of chromatins are formed. The occurrences of univalents,
trivalents, quatrivalents and multivalents together with bivalents have
been observed in Excoecaria agallocha and Manihot utilissima.
Mitotic and meiotic abnormalities in the form of anaphasic
laggards and bridges have been observed in Pedilanthus tithymaloides,
Emblica officinalis, Euphorbia hirta, Ricinus communis and Hevea
brasiliensis (Table-10). These abnormalities may be the sequence of
inversion heterozygosity of gametophytic cells (Upcott, 1937). These
meiotic abnormalities may also be transmitted to the mitotic divisions.
The inversion heterozygosity is known to cause univalency to some
extent in various species of Citrus (Raghuvanshi, 1962), as the presence
of inversion presents regular pairing and chiasma formation. The
univalents formed lag behind as anaphasic laggards or they link together
to form a bridge. Higher temperature induces the formations of
univalents (Dowrick (1957); Sax (1937) and Utkhede and Jain, 1974).
Genetical factors may be responsible for the formation of univalents in
more number, as indicated by the contributions of Beadle (1932).
The early prophasic stage namely “Zygotene” reveals bouquet
configuration of the chromosomes and this is presumably due to
approximation of the chromosomes towards the nucleus (Digby, 1919).
This condition has been often taken to be an artifact brought about by
the collapsing action of fixatives, but in the material under investigation
such synizetic knot of convoluted chromatin threads looking like a
tangled skin of fibres has been observed even where the anther was
teased in dilute glycerine. This would appear perhaps to support the idea
that the synizetic knot is an inherent behavior actually rather than a
mere artifact.
5.5. Presence of B-chromosomes
Three species of Euphorbiaceae studied possess ‘B’ chromosome
and of these, all of them are polyploids. The number of ‘B’ chromosomes
may vary from 4 to 6 (Table-14, 25 and 26). The species with ‘B’
chromosomes are 1) Chrozophora rottleri 4 B 2) Manihot utilissima 4 B
and 3) Excoecaria agallocha 6 B.
In Excoecaria agallocha “B” chromosomes have been observed in
both mitosis and meiosis. In mitosis, the ‘B’ chromosomes have been
observed from prophase to telophase, in the form of precocious
movement of chromosomal portion during metaphase and lagging
chromosomes during
anaphase and telophase. In meiosis, these ‘B’
chromosomes have been noted as laggards during telophase I.
According to Sharma (1978), this redundancy of heterochromatin
resulting in compaction and shortening of chromosome size, can be
extended to the behavior of accessory chromosomes which represent
mostly a cytological embodiment of heterochromatin and show analogous
behavior. From a detailed survey, Darlington (1956) first suggested that
“B” chromosomes or accessories are found mostly in diploids as
compared to polyploids. In Urginea indica as well diploid individuals
possess “B” chromosomes whereas, the polyploids do not (Sen, 1974).
Even though there are reports of euchromatic “B” Chromosome the
majority are heterochromatin in nature (Muntzing (1974); Jones (1975)
and Dover, 1975). In Allium stracheyii of the Eastern Himalayas, Sharma
and Aiyangar (1961) recorded the occurrence up to 8 ‘B’ chromosomes
in diploids and their complete absence in polyploidy individuals of the
same species. These diploid individuals, grown under tropical conditions,
were gradually converted into polyploids with the complete elimination of
“B” chromosomes. Induction of polyploidy and subsequent elimination of
“B” have been avoided by growing plants in artificial environment with
lower temperature, representing the Himalayan conditions (Sharma and
Aiyangar,1961). This behavior is taken as an index that ‘B’ Chromosomes
confer certain adaptive advantage at the diploid level. With the tolerance
of the species through increased gene dosage, they became redundant
and are eliminated. Selective destruction of DNA and regulation by
chromosome elimination or heterochromatization have been observed by
other authors as well (Sager and Kitchin, 1975).
5.6. Cyto-taxonomical considerations
The family Euphorbiaceae starts with the genus Euphorbia, that
are herbs, shrubs and some trees of various habit and with copious
milky, usually acrid juice. Inflorescence of many pedicelled bracteolate
stamens as male flowers surrounding a single pedicelled female, the
whole contained in a 4-5 lobed involucres. In Euphorbia, involucres
regular or nearly so whereas, involucres obliquely zygomorphous in
Pedilanthus. Of the three species studied in Euphorbia, Euphorbia hirta,
is a straggling ascending hispid herb reaching up to 2 feet high.
Euphorbia tirucalli is a large shrub, with very small flower, the bracteoles
among the male laciniate at tip; wood hard, said to give a good powder
charcoal. Euphorbia splendens is a small prickly very much branched
shrub with showy crimson flower common in gardens in the plains.
These species are characterised by monoecious flowers combined in
inflorescences of many male florets surrounding a solitary female.
Cytologically these species possesses 2n=20 (Euphorbia hirta; Euphorbia
tirucalli) and 2n=40 (Euphorbia splendens); chromosomes. All the three
species have latex in their vegetative organs. Cytologically, except
Euphorbia splendens the other two species have secondary constricted
chromosomes. Cytologically, Euphorbia splendens is unique in the sense
it has sub-terminal chromosomes with tetraploids 2n=4x=40.
In
Pedilanthus
tithymaloides
four
secondary
constricted
chromosomes and six sub-terminal chromosomes are present. The
somatic chromosome number is 2n=36. This species is different from
Euphorbia, in the presence of cyathium distinctly bilaterally Symmetrical,
glands hidden within a well developed nectar spur. But in Euphorbia
cyathium radially symmetrical, glands inserted on outside of cyathium.
The three species of Phyllanthus studied namely Phyllanthus niruri,
Phyllanthus acidus and Phyllanthus myrtifolius are herb and shrubs, with
slight morphological variations among them. Phyllanthus niruri is a herb
with membranous leaves broadly obtuse at apex, very variable in size but
usually under 0.5 inch long. It is often used in native medicine.
Phyllanthus acidus is a shrub, presumably cultivated for its edible fruits.
In these two species, the somatic chromosome numbers is the same, that
is, 2n=26. Phyllanthus myrtifolius is a large shrub with 2n=52
chromosomes; a tetraploid species (2n=4x=52). Plants monoecious.
Inflorescence are axillary several flowered fascicle; pedicels filamentous,
unequal, 3-5 mm. Male and female flowers are distinctly present in the
same plant. Capsule fruit with 3 - angled seed is characteristic of
Phyllanthus myrtifolius. It is cultivated for medicine.
Emblica officinalis is a large tree, monoecious, deciduous, with
reduced short group of leafy shoots. Male and female flowers are distinct
with globose drupe fruit, 1-1.5 cm in diameter, rich in vitamin C. The
somatic chromosome number is 2n=98 in this species and no other
species studied has this diploid number of chromosomes. This species is
also characterised by the presence of secondary constricted chromosome
with 18 sub-terminal chromosomes. This species is a polyploidy in
occurrence with (2n=7x=98) (x=4) aneuploidy polyploids.
The species of Sauropus androgynus is a shrub with monoecious
flowers it is commonly called multivitamin plants, since, the leaves are
edible. Cytologically this species has 2n=24 chromosomes and it differs
from the species of Aporosa lindleyana and Baccaurea courtallensis;
which possess 2n=52; 2n=36 chromosomes respectively. All the three
Genera have secondary constricted chromosomes, uniformly six number
in each taxon. Further, Morphologically Aporosa lindleyana is a medium
sized evergreen tree with coriaceous leaves. Flower dioecious, male
minute, clustered catkin-like spikes and female in short bracteate spikes.
Fruit a globose capsule with oblong seeds. Baccaurea courtallensis is also
an ever green tree remarkable for the flowers growing in long racemose
spikes in tuffs on tubercles on the stems and branches, often, “in great
profusion, the whole trunk appearing as a crimson mass”. Fruits
crimson, about one inch in diameter; edible. In studying all the three
species, morphologically and cytologically they are distinct and different
among
themselves
with
reference
to
habit,
habitat
and
diploid
chromosome numbers.
Croton variegatum and Croton sparsiflorus both have the somatic
chromosome number is 2n=64, with secondary constricted chromosomes
and sub-terminal chromosomes. But morphologically, they differ chiefly.
Croton variegatum, is a large shrub and Croton sparsiflorus is a herb;
they show their species specificity. Both species are cytologically similar
but morphologically different.
Chrozophora rottleri, Acalypha indica, Acalypha fruticosa and
Ricinus communis differ among themselves in morphological characters
particularly in the nature of habit, habitat, inflorescences and flowers.
Chrozophora rottleri has 2n=44 chromosomes; Acalypha indica 2n=20;
Acalypha
fruticosa
2n=20
and
Ricinus
communis
2n=20.
Except
Chrozophora rottleri, all the three species have 2n=20 chromosomes with
S, J, V type of chromosomes. In Chrozophora rottleri the diploid
chromosome number is 2n=44 with the presence of ‘B’ chromosomes but
with the absence of secondary constricted chromosomes. Cytologically
Chrozophora rottleri differs from the other three taxa in the absence of
secondary constricted chromosomes.
The species of Jatropha studied namely Jatropha glandulifera,
Jatropha gossypifolia, Jatropha curcas and Jatropha multifida are large
shrubs or small trees. The somatic chromosome number in all the
species of Jatropha studied are 2n=22 with secondary constricted
chromosomes and sub-terminal chromosomes. Morphologically they
differ among themselves by the presence of flowers greenish yellow in
Jatropha glandulifera; reddish flower in Jatropha gossypifolia; yellowish
green in Jatropha curcas and bright red flowers in Jatropha multifida. In
comparing all the four species of Jatropha, Jatropha curcas is very useful
in medicine and bio diesel crop where the seeds have yielded oil
cultivated in Indian and other tropical countries for seed harvest.
Hevea brasiliensis; Manihot utilissima and Excoecaria agallocha
differ among themselves in morphological characters, particularly in the
nature of habit, habitat, inflorescence and flowers. Hevea brasiliensis has
2n=72 chromosomes and absence of ‘B’ chromosomes is unique and
species specific and differ from the other two taxa, have the same diploid
somatic chromosome number, but with the presence of ‘B’ chromosomes.
Characteristically
all
the
three
taxa
have
secondary
constricted
chromosomes. Further all the three species have potential economic
values, Hevea as Rubber yielding, Manihot as starch yielding and
Excoecaria as latex yielding with specific utilization. The habitat of Hevea
brasiliensis is along the river bank in its native home; Brazil of America,
whereas as in other parts of world, it may be well grown in mountainous
region. Similarly the habitat of Manihot utilissima is mesophytic, and the
roots are modified into tuberous form, where the photosynthetic
products are stored as starch. Again the habitat of Excoecaria agallocha
is in brackish water, tidal forests and swamps on both coasts. It is an
evergreen tree with a poisonous milky juice. This plant is considered as a
Temple tree (It is planted in Lord Nataraja Temple of Chidambaram,
Tamil Nadu, India).
On the basis of the present cytotaxonomical consideration the
following 7 group may be recognized, the first group with Euphorbia hirta,
Euphorbia tirucalli, Euphorbia splendens and Pedilanthus tithymaloides,
the
second
group
with
Phyllanthus
niruri,
Phyllanthus
acidus,
Phyllanthus myrtifolius and Emblica officinalis, the third group with
Sauropus androgynus, Aporosa lindleyana and Baccaurea courtallensis,
the fourth group with Croton variegatum and Croton sparsiflorus; the fifth
group with Chrozophora rottleri, Acalypha indica, Acalypha fruticosa and
Ricinus communis; the sixth group with Jatropha glandulifera, Jatropha
gossypifolia, Jatropha curcas and Jatropha multifida and the seventh
group with Hevea brasiliensis, Manihot utilissima and Excoecaria
agallocha. Therefore, the cytotaxonomical studies clearly show that these
24 taxa studied reveal the polyphyletic nature of origin and evolution.
Only by the presence of mostly 10 and 11 basic chromosome numbers
and by the presence of milky juice, latex and oil from seeds inflorescence
axillary or terminal, flowers in cymes or fascicles they are arranged along
an elongated axis, branched axis, in congested heads or in a flower like
cyathium with reduced flowers enclosed within a ± cupular involucre
bracts sometimes petaloid, by which the species of Euphorbiaceae are
linked together forming a particular family.
5.7. Palynological aspects:
No detailed palynological studies have been so far made in the
South Indian species of Euphorbiaceae. In this present investigation
some detailed studies such as pollen size and shape classification have
been made. The knowledge of pollen studies has been impacted by many
authors like Chennaveeraiah and Shivakumar (1982) in Ophiorrhiza,
Vasanthy (1976) on the pollen of south Indian Hills and Sreenivasan
et al., (1975), in differential staining of pollen and pollen tubes in coffee.
The universal centrifuge and acetolysis method of pollen preparation had
its possible success by noble touch of Wodehouse (1935) and Erdtman
(1945).
The
species
of
Euphorbiaceae
studied
possess
tricolpate,
tetracolpate and polycolpate pollen grains. In the uniform presence of
granular wall ornamentation of pollen grains, the various species of the
Euphorbiaceae are linked together. The occurrence of tri or tetra or
polycolpate pollen grains is an advanced character (Erdtman, 1945) of
the family. In the species of Euphorbia studied almost all the types of
pollen grains occur, showing the gradation of multifarious types of pollen
grains, even among the species of particular genus. The species of
Oldenlandia are not related together among themselves as far as the
palynological studied are concerned. On the other hand, the species of
Phyllanthus are related together among themselves, as evidenced by the
present palynological studies. Similarly, Croton variegatum and Croton
sparsiflorus are related together. Acalypha indica and A. fruticosa are
related together. Therefore, it may be clear that the above taxa are
related together at species level. On the other hand, the species of
Jatropha
namely,
J.
glandulifera,
J.
gossypifolia,
J.
curcas
and
J. multifida are not so much related together. When we consider the
relationship at generic level, each and every genus is distinct as
evidenced by the present observations. Therefore, it is concluded that the
taxa studied are polyphyletic in nature, although they assigned to a
particular family.
5.8. Leaf anatomical basis of taxonomical relationship
There are several elaborate works of leaf anatomical studies
including foliar epidermal studies, by different authors. Such studies
have been successfully utilized to solve the problems of taxonomical
interrelationship of plants. Ramona Crina Gales and Constantia Toma
(2006); Selvaraj and Aruna Devi (2000); Essiett et al., (2012); Takur and
Patil (2011); Maria Bernadete Gonclaves Martins and Rodrigo Zieri
(2003); Idu et al., (2009); Aworinde et al., (2009) and many others.
In the present investigation, an attempt has been made to study
comparatively the leaf anatomical characteristics of 24 taxa of South
Indian Euphorbiaceae. The following characters are observed and
concluded that the 24 taxa of Euphorbiaceae studied show the
polyphyletic
nature
of
evolutionary
significance
and
supporting
additional evidence for the main frame of Cytotaxonomical studies.
1. Thick cuticle are observed in all the species studied here.
2. In upper epidermis single row of epidermal cells (parenchyma)
occur
in
all
the
species
studied
except
Pedilanthus
tithymaloides, Acalypha fruticosa, Ricinus communis, Jatropha
glandulifera and Manihot utilissima; where they are two or three
rows.
3. The mesophyll tissues are differentiated into palisade and
spongy parenchyma in all the species studied here except,
Euphorbia tirucalli and Aporosa lindleyana. In the two species
(Euphorbia tirucalli and Aporosa lindleyana); the mesophyll
tissue are only spongy parenchyma.
4. The occurrence of single row of palisade parenchyma have been
observed in all the species of Euphorbiaceae studied here,
except Euphorbia splendens; Pedilanthus tithymaloides; Croton
variegatum; Acalypha fruticosa; Jatropha glandulifera; Jatropha
curcas; Jatropha gossypifolia; Jatropha multifida and Excoecaria
agallocha. In all the above mentioned species, there are two or
rarely three rows of palisade parenchyma cells present, to
enhance the photosynthetic rate and efficiency; for quick growth
and regeneration.
5. In Chrozophora rottleri, the occurrence of palisade parenchyma
on both sides of the lamina surfaces (Upper and Lower side) and
spongy parenchyma and vascular bundles are occurring in
between them. Hence, Chrozophora rottleri, is considered as
unique with regards to mesophyll tissue distribution.
6. The vascular bundles in mid-vein, lateral vein in the mesophyll
tissues and in the lamina surfaces are uniform throughout the
various species of Euphorbiaceae, studied here.
7. The latex, laticiferous tissues, latex vessel and resinous ducts
are familiar in this family Euphorbiaceae (Hevea, Jatropha and
Excoecaria).
8. All the species studied here, showed Rubiaceous type of
stomatal distribution (Paracytic type), with rare occurrence of
anisocytic
and
anomocytic
type
in
few
species
of
the
angiospermic family Euphorbiaceae.
5.9. Epidermal basis of taxonomical relationship
There are several elaborate works of epidermal characters by
different authors. Such studies have been successfully utilized to solve
the problem of taxonomical interrelationship of plants. Ramayya and
Raja Shanmukha Rao (1976); Raja Shanmukha rao and Ramayya (1977);
Bates (1967) and Jain and Singh (1973) have studied the morphology,
phylesis, trichome nature, stomatal nature and epidermal cells of the
various species of the family Malvaceae. Ahmad (1976); Inamdar (1967)
and King and Robinson (1970) have studied the epidermal characteristics
of the species of Acanthaceae. The works of the epidermal feature by
Inamdar (1967) in Oleaceae and King and Robinson (1970) and Ramayya
(1962) in Eupatorium (Compositae) are helpful in solving taxonomical
problems. In the present investigation, an attempt has been made to
study comparatively the epidermal characteristic of 24 taxa of south
Indian Euphorbiaceae (Table-28 and 28a)
All the species of Euphorbiaceae studied are linked together by
uniform presence of paracytic type of stomata, with occasional or
frequent disturbances of anomocytic and anisocytic type of stomata in
the same species or different species of the same genus. Even though, we
may separate these taxa into 2 major divisions by what is known as the
characters such as amphistomatic and hypostomatic condition, it is not
positive to come to a fundamental conclusion by classifying the taxa into
a definite number of groups on the basis of epidermal characteristics. For
instance among the four species of Jatropha studied, two species namely
Jatropha glandulifera and Jatropha curcas possess amphistomatic
condition whereas Jaatropha gossypifolia and Jatropha multifida have
hypostomatic condition. There are variations in the stomatal frequency of
lower epidermis among the species of Jatropha. Jatropha glandulifera 23;
Jatropha gossypifolia 34; Jatropha curcas 15 and Jatropha multifida 05.
On the other hand, the three taxa of Euphorbia, Euphorbia hirta;
Euphorbia
tirucalli
and
Euphorbia
splendens
possess
uniformly
hypostomatic condition. There are only two categories of stomatal
frequency (Euphorbia hirta 28; Euphorbia tirucalli and Euphorbia
splendens 20). The species of Phyllanthus emblica, Sauropus, Aporosa,
Baccaurea, Croton, Acalypha, Hevea, Manihot and Excoecaria studied
show hypostomatic condition, where as the species of Croton, Croton
variegatum show hypostomatic condition and Croton sparsiflorus show
amphistomatic condition. Therefore, it is concluded that among the
species of Euphorbiaceae studied, there is no correlation between the
number of stomata and epidermal cells as evidenced by the studied by
stomatal frequency.
Each and every species studied is more or less distinct and it is
even difficult to classify them on the basis of epidermal characteristic.
For instance, the highest stomatal frequency of stomata of lower
epidermis among the 24 species of Euphorbiaceae studied shows a range
of 05 to 36 and this range is represented by a large number of species
coming under different genera. (Phyllanthus niruri 18; Phyllanthus acidus
20;
Phyllanthus
myrtifolius
19;
Emblica
officinalis
22;
Sauropus
androgynus 21; Aporosa lindleyana 10; Baccaurea courtallensis 10;
Chrozophora rottleri 36; Acalypha indica 26; Acalypha fruticosa 23;
Ricinus communis 20; Manihot utilissima 24 and Excoecaria agallocha 26
(Table-28 and 28a). The present epidermal studies show that the taxa
studied are polyphyletic in nature.
PLATE-10
MITOTIC ABNORMALITIES (X2000)
1
4
2
5
3
6
8
7
9
10
PLATE-10
MITOTIC ABNORMALITIES (X2000-PHOTOS)
EXPLANATION OF PLATE
1. Euphorbia hirta Linn.
- Anaphasic bridges and sticky chromosomes.
2. Pedilanthus tithymaloides (L.) Poit. - Telophasic bridges and sticky
chromosomes.
3. Emblica officinalis Gaertn.
- Telophasic bridges- multiple bridges.
4. Croton variegatum Linn.
- Telophasic bridges between two cells
5. Croton variegatum Linn.
- Telophasic bridges between three cells
6. Ricinus communis Linn.
- Telophasic laggard
7. Hevea brasiliensis Muell. Arg. - Telophasic laggard
8. Jatropha curcas Linn.
- Precocious movement of chromosome
9. Jatropha multifida Linn.
- Telophasic laggards
10. Excoecaria agallocha Linn.
- Telophasic bridges
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FIGURE-9
SCHEMATIC
REPRESENTATION
OF
THE
EVOLUTIONARY
RELATIONSHIP OF CHROMOSOME NUMBER OF THE VARIOUS
SPECIES OF EUPHORBIACEAE
Higher polyploidy
49
36
32
2
Aneuploidy
18
Nullisomic
(-2)
26
24
22
Euploidy
doubling
20
10
11
12
13
3
Haploid chromosome number