NATURA MONTENEGRINA, PODGORICA, 6: 9-17
VARIATION IN THE ANATOMY OF THE VASCULAR SYSTEM
OF Asplenium trichomanes-ramosum L.
Rodica B E R C U 1
1
Department of Botany, Faculty of Natural and Agriculture Sciences, “Ovidius” University,
Mamaia Str. 124, 900590, Constantza, Romania, E-mail: [email protected]
Key words:
SYNOPSIS
anatomy,
variation,
vascular system,
estimation,
Asplenium trichomanesramosum
The paper provides new data regarding the variation of the
vascular system in the vegetative organs of Asplenium trichomanesramosum L. The anatomical structure of the adventitious root
(starting up directly from the underground stem), rhizome (stem)
and the frond’s petiole and rachis exhibit a diarch type root, a
dictyostelic rhizome and an X- and T-shaped petiole and rachis
vascular system up to the subterminal rachis. Based on the variation
of the vascular system in A. trichomanes-ramosum anatomy we
used a mathematical calculation to estimate the number of the
vascular bundles in the fern vegetative organs.
INTRODUCTION
Asplenium trichomanes-ramosum L. (syn. A. viride Huds.), known as bright
green spleenwort or simple green spleenwort, is a perennial member of family A
spleniaceae. The branching rhizomes are short, creeping to erect, bearing dark brown
to black scales (C i o c a r l a n , 2000). The evergreen compound fronds, simply divided
are tufted at the crown, 4–15 (-20) cm long; persistent to dying in the autumn and
circinnate. The frond’s rachis is green and not winged.
The petioles are often shorter than the blade. The petioles are brownish or
blackish only near the base and green above. It grows in spring and fructifies in
summer. The leaves disappear slowly during the next spring (W a t s o n . &
D a l l w i t z , 2004).
In Romania it grows in shaded crevices of limestone boulders, cool and moist
places, up to an altitude above 1800m (S a v u l e s c u , 1952). Knowledge on the
variations of the vascular system organization of the fern vegetative organs is quite
limited (O g u r a , 1938, 1972, S c h n e i d e r , 1996), and that of A. trichomanes-
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ramosum L. is almost lacking. The goal of the research was to examine the anatomy
of the adventitious root, rhizome, and frond’s petiole and rachis in order to find a
mathematical distribution function to estimate the number of the vascular bundles in
the fern vegetative organs in accordance with plant morphology, habitat and the
cutting level.
MATERIAL AND METHODS
The plant was collected from the Bicaz Gorges in the Carpathians Mountains.
Cross sections of the adventitious root, rhizome and the frond’s petiole and rachis of
A. trichomnaes-ramosum were performed using a rotary microtome. The petiole and
rachis structure were analyzed by serial cross sections (2 to 2 cm), distributed from
the base up to the rachis tip. The samples were stained with alum-carmine and iodine
green and were embedded in Canada balsam. Observations were made with a
BIOROM-T bright field microscope, equipped with a TOPICA-6001A video camera.
The microphotographs were obtained from the video camera through a computer.
RESULTS AND DISCUSSION
Cross sections of the adventitious root revealed that the cortex is composed of
2-3 layers of large parenchyma cells (Fig. 1). The inner cells of the cortex are
modified and have thick walls. Kroemer (1903) has suggested that this wall thickening
is the result of cutinized blade superpositions. Some authors have noticed the
presence of such “curious cells” around the stele and have suggested that this tissue
belonged to the stele naming it “sclerenchymatous mass” (R u s s o w 1872,
B i e r h o r s t 1971) or a “stereomic sheath” (de B a r y 1877, O g u r a 1938, B e r c u
1998, 2006). This configuration has led S c h n e i d e r (1996) to ascribe this type of
root to that of Asplenium. The stele consists of xylem and phloem and is surrounded
by the pericycle (Fig. 1). The xylem vessels are joined together towards the center by
their metaxylem vessels (two for each bundle). The protoxylem vessels (three for each
bundle) are in an exarch position and face the pericycle. The phloem sieve cells,
lacking companion cells, are located on either side of the xylem string. Thus the
adventitious root of A. trichomanes-ramosum has a diarch structure. Remarkable are
the passing cells (Fig. 1).
Cross sections of the rhizome disclosed that the epidermis consists of a single
layer of cells not covered by cuticle (Fig. 2A). Below the epidermis is the cortex,
differentiated into a sclerenchyma cortex and the inner cortex, the latter consisting of
large parenchyma cells. Remarkable is the abundance of starch grains in the cortical
cells and endodermis as well (amiliferous sheath) (Fig. 2B). As O g u r a (1938) and
B i r (1957) reported for Aspleniaceae species, the stele is a dictyostele composed of
a variable number of meristeles (in accordance with the number of foliar traces) each
surrounded by its own endodermis (starch sheath) and pericycle. The latter is
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composed of parenchyma cells regularly arranged in one row, (locally in two or even
three rows). Each meristeles is hadrocentric with a binary structure (metaxylem
vessels towards the center and protoxylem elements facing the pericycle). The pith
rays among the meristeles occur. The pith occupies the central area of the rhizome
(Fig. 2B).
Fig. 1. Cross section of the adventitious
root, x 206: C- cortex; Mx- metaxylem; Pcpericycle; Ph- phloem; Px- protoxilem; SSsclerenchyma sheath.
Fig 2. Cross sections of the rhizome. (A). Portion of the epidermis, cortex and stele, x 160: Ccortex, E – epidermis, GT – ground tissue, M- meristeles, Pi- pith, PiR- pith ray. (B) A stele
vascular bundle (meristele), x 212: Ed- endodermis, Mx- metaxylem, Pc- pericycle, Ph- phloem, Pxprotoxylem.
Cross section of the petiole base exhibits an epidermis, the cortex differentiated
into an external (sclerenchzmatous) and an inner cortex, followed by a ground tissue.
The vascular system of the leaf petiole base is composed of two meristeles, equal in
size (distele). Each meristele is surrounded by an endodermis and a “special
pericycle” (A n d r e i , 1978). The meristeles are composed of centrally located xylem
elements surrounded by phloem. Protoxylem vessels are in an exarch position
whereas the metaxylem vessels are in the centre. That is attributed to the stele a
hadrocentric and distelic structure (Fig. 3).
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Fig. 3 Cross section of the leaf petiole
base, x 83: E- epidermis, GT- ground
tissue, IC- inner cortex, M- meristele,
SC- sclerenchyma cortex.
Fig. 4 Cross section of the leaf petiole (2 cm from the leaf base). (A) General view, x 64: C- cortex,
E- epidermis, St- stele. (B) Portion of epidermis and cortex, x 272: E- epidermis, IC- inner cortex,
SC-sclerenchymatic cortex. (C) The stele vascular bundle, x 266: Ed- endodermis, Pc- pericycle, Phphloem, Mx- metaxylem, Px- protoxylem.
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Transverse sections of the petiole, cut from 2 cm above the leaf base, reveals a
single-layered epidermis, covered by cuticle, a cortex and a centrally located stele
(Fig. 4A). Below the epidermis of the base of the petiole is the sclerenchyma cortex
(hypodermis), which consists of a few layers of compactly arranged sclerenchyma
cells. The hypodermis is internally followed by a region of ground tissue (Fig. 4B). The
stele is monofascicular. The vascular bundle is composed of centrally located xylem
vessels surrounded by phloem. The stele X-shaped xylem elements possesses
themetaxylem vessels in a central position and the protoxylem elements in an exarch
arrangement, surrounded by phloem. That is attributed to the stele a hadrocentric
structure (Fig. 4C).
Cross sections of the rachis cut from 3-8 cm above the leaf petiole disclosed the
same one-layered epidermis composed of cutinized-walled cells, covered by a thick
cuticle, a cortex and a stele. The stele is monofascicular, composed of more or less Tshaped xylem vessels (meta- and protoxylem vessels) characteristic to most of the
Aspleniaceae species (O g u r a 1972, B i r 1957; B e r c u 2004, 2005). Phloem
surrounds the xylem elements as well (Fig. 5). Toward the subterminal leaf rachis
remarkable is the reduced number of the vascular elements, surrounded by phloem
and embedded in a homogenous mesophyll (Fig. 5A, C). The vascular elements are in
a reduced number because of the veins marginal segments formation. Under the lower
and upper epiderms of the rachis, sclerenchyma cells are present. They provide
mechanical support to the weak and delicate rachis tip. A typical hypodermis is
absent.
Fig. 5 Cross section of the leaf rachis (3-8 cm
above the leaf rachis), x 300.
A. trichomanes-ramosum vegetative organs anatomy exhibits variations in the
vascular system organization. The even and odd number of the vascular bundles
(meristeles) may depend by the plant size, and organs diameter, the plant habitat
ecotope and the cutting level. The mathematical distribution function takes into
account of the ecological parameters such as soil humidity (U), temperature (T) and
soil reaction – pH (R) (Table 1) settled by P o p e s c u and S a n d a (1998). The
distribution function was based on S ă h l e a n u (1957), C e a p o i u (1968), S i r e ţ c h i
(1985) and N a s t a s e s c u et al. (1988) works.
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The root (r) – the diameter = 0,1-0,5 mm:
r
N Aspl. t-r . = (2n+1) K (a+b+c) πD 2
4e h
= 5 ·10 · 3,14 · 0,44 2 = 30,3954
29,6
= 1,028 ≈ 1 stele
29,6
The rhizome (rz) – the diameter = 1-1,5cm:
rz
N Aspl. t-r = (2n+1) K (a+b+c) πD 2
3 ·10 · 3,14 · 1,26 2 = 149,55 = 5,06 ≈ 5 meristeles
=
h
29,6
29,6
4e
The rachis (rh) – the diameter = 0,5-1 mm:
pt. base
a.
N Aspl. t-r . = 2n K (a+b+c) πD 2 = 2 ·2·10· 3,14 · 0,69 2 = 59,798
4e h
29,6
29,6
= 2,02 ≈ 2 meristeles
rh
b. N Aspl. t-r . = (2n +1) K (a+b+c) πD 2 = 3 ·10· 3,14 · 0,92 2 = 79,73
4e h
4 · 2,71 3
78,732
= 1,01 ≈ 1 meristele
Where:
r, rz, pt. base, rh
N Aspl. t-r .– the function distribution of the vascular bundles in root (r), rhizome
(rz), petiole base (pt. base) and rachis (rh);
h – the distance (in cm) between two succesive sections;
D – the vegetative organs diameter of the plant (in mm);
e – the natural logarithm base (e = 2, 718);
K (a+b+c) – the ecological constant of the plant depending of: humidity (a),
temperature (b) and soil reaction (c);
n – the multiplication order;
2n – the even number of the vascular bundles;
2n+1 – the odd number of the vascular bundles.
NOTE: it is sufficient the estimation of
r, rz, pt. base, rh
N As t-r.
only for n=1 sau n=2 value.
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Table 1: The ecological preferences of A. trichomanes-ramosum
Ecological parameters
The species
Asplenium
trichomanesramosum L.
humidity
(H)
temperature
(T)
soil reaction
(R)
mesohydrophyte
4
microtermous
2
Slightly neutroacidophilous
4
*The value of the
ecological constant
(K(a+b+c))
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CONCLUSIONS
The successive cross sections, cut from the rhizome and the frond’s petiole and
rachis of A. trichomanes-ramosum L. disclose variations in the vascular system
structure. The root is of diarch type. The rhizome is a dictyostele with a variable
number of meristeles due to the number of the foliar traces. The petiole base vascular
system is bifascicular whereas from 2 cm above the petiole base up to the rachis tip
the vascular system is monostelic, first X-shaped and then T-shaped (to the tip).
These expected results based on any earlier research permited us to find a
mathematical distribution function to estimate the number of the vascular bundles in
the fern vegetative organs in accordance with the plant size, the organs diameter, the
main habitat plant factors and the cutting level. The distribution formula can be
extended to other members of this large group of plants.
LITERATURE
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Bucharest, p. 227-229 (in Romanian).
B E R C U , R . (1998): Anatomical Modifications of the Corm Stele in Fern Asplenium
septentrionale (L.) Hoffm. - Forestry, Sumarstvo, Belgrade 1: 35-40.
B E R C U , R . 2004: Anatomical Aspects of Asplenium adiantum-nigrum L. - J. of Biol. Res.,
vol. 2: 57-61.
B E R C U , R . 2005: Anatomy of Asplenium ruta muraria L. - Studia bot. hung., vol. 36: 16-20.
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B I E R H O R S T , D . W . 1971: Morphology of Vascular Plants. Collier - Macmillan Ldt.,
Macmillan Co. London, New York, 296-298, 300-304.
B I R , S . S . 1957: Stelar anatomy of indian Aspleniaceae, Abstract. - Proc. Ind. Sci. Congr.
Association, Calcuta, 44: 232.
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C E A P O I U , N . 1968: Statistics methods applied in agricultural and biological experiences.
- Agro-Silvica Publishing House, Bucharest, p.201-203 (in Romanian).
C I O C Â R L A N , V . 2000: Ilustred Flora of Romania - Pteridophyta et Spermatophyta. II
edition, Ceres, Bucharest, p.90-92 (in Romanian).
d e B A R Y , A . 1877: Verigleichende Anatomie der Vegetationsorgane der Phanerogamen
und Farne. - W. Engelmann, Leipzig, p.238-349 (in German)
K R O E M E R , K. 1903: Wurzelhaut, Hypodermis und Endodermis der Angiospermenwurzel. Biblioth. Bot., 12: 151 (in German).
NASTASESCU, C., TENA, M., ANDREI Gh. and OTRASANU, I.
1988: Problems of Algebraical Structures. - Reip. Pop. Romanian Acad., Bucharest,
p.122-125 (in Romanian).
O G U R A , Y . 1938: Anatomie der Vegetationsorgane der Pteridophyten. In: Handbuch der
Pflanzeanatomie, Gebrüder Borntraeger, Berlin, p.128-140 (in German).
O G U R A , Y . 1972: Comparative Anatomy of Vegetative Organs of Pteridophytes, II edition,
Gebrüder Borntraeger, Berlin, Stuttgart, p.313-512.
P O P E S C U , A a n d S A N D A , V . 1998: The Summary of the Spontaneous
Cormophytes from the Romanian Flora. - Acta Bot Horti., Bucharest, p.4-7 (in Romanian).
R U S S O W , E . 1872: Vergleichende Untersuchungen betreffend die Histologie der
vegetativen und sporenbildenden Organe und die Entwicklung der Sporen der LeitbündelKryptogamen. Mém. Acad. Imp. Sc., St. Petersbourg, Sér. VII, 19: 1-207 (in German).
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Summary
VARIATION IN THE ANATOMY OF THE VASCULAR SYSTEM
OF ASPLENIUM TRICHOMANES-RAMOSUM L.
In Romania Asplenium trichomanes-ramosum L. grows in shaded crevices of
limestone boulders, cool and moist places, up to an altitude above 1800m. The goal of
the research was to examine the anatomy of the adventitious root, rhizome, and
frond’s petiole and rachis in order to find a mathematical distribution function to
17
B e r c u : VARIATION IN THE ANATOMY OF THE VASCULAR SYSTEM …
estimate the number of the vascular bundles in the fern vegetative organs in
accordance with the plant morphology, habitat and the cutting level.
The root, in cross section possesses a primary structure and the stele is a diarh
one. Remarkable is the sclerenchimatous sheet around the stele (Fig. 1).
Cross section of the rhizome discloses a single layered epidermis (Fig. 2A),
cortex, differentiated into a sclerenchyma cortex and the inner cortex, the latter
consisting of large parenchyma cells consisting of numerous starch grains followed by
an amiliferous sheath (Fig. 2B). The stele is a dictyostele composed of a variable
number of meristeles (in accordance with the number of foliar traces) each surrounded
by its own endodermis and pericycle. Each meristeles is hadrocentric with a binary
structure (metaxylem vessels towards the center and protoxylem elements facing the
pericycle). The pith rays among the meristeles occur. The pith occupies the central
area of the rhizome(Fig. 2B, C). The frond’s petiole and rachis were analyzed by serial
cross sections (2 to 2 cm), distributed from the base up to the rachis tip. The petiole
base vascular system is bifascicular whereas from 2 cm above the petiole base up to
the rachis tip the vascular system is monostelic, first X-shaped and then T-shaped (to
the tip). These expected results based on any earlier research permited us to find a
mathematical distribution function to estimate the number of the vascular bundles in
the fern vegetative organs in accordance with the plant size, the organs diameter, the
main habitat plant factors and the cutting level.
Received: 26. 11. 2007.
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