Analele ştiinţifice ale Universităţii “Al. I. Cuza” Iaşi
Tomul LV, fasc. 1, s.II a. Biologie vegetală, 2009
DROSERA CAPENSIS L.: HISTO-ANATOMY OF THE VEGETATIVE ORGANS
IRINA STĂNESCU*, C. TOMA**
Abstract. The investigated species (Drosera capensis L. and three forms: D. capensis L. ‘Alba’, D.
capensis L. ‘Narrow Leaf’ and D. capensis L. ‘Rubra’) show common characters, regarding the structure
of the vascular bundles, the type of stomata, the presence of the secretory trichomes, the homogenous
mesophyll. The species present different quantities of a red pigment in the head of the tentacles which
makes them attractive for the insects.
Key words: vegetative organs, stalked trichomes
Introduction
Drosera, known as sundews, represents one of the largest genera of carnivorous
plants. They grow in a poor mineral soil, but they show a great variety of physical
characteristics and adaptations [1 and 2]. The structure of the leaves, their shape and unique
elements pay for out attention. The sundews use insects or other small animals to
supplement their nutrition, helped by the stalked mucilaginous glands (tentacles) which
cover their leaf surface. Drosera species are spread all over the world, except Antarctica.
The paper is focused on the anatomy of Drosera capensis L. known as the Cape
sundew, which belongs to the cape area of South Africa and its forms D. capensis L. ‘Alba’,
D. capensis L. ‘Narrow Leaf’ and D. capensis L. ‘Rubra’. In D. capensis, the head of the
mature tentacles contains a red pigment which makes them attractive for the insects; the
young (immature) tentacles contain the same pigment, but in a smaller quantity. The same
aspect is present in D. capensis L. ‘Narrow Leaf’ and D. capensis L. ‘Rubra’. In D.
capensis L. both petiole and head of the tentacles are green (do not present the red
pigment).
Material and methods
The material subjected to the histological analysis (the vegetative organs of Drosera
capensis L. (Fig. 1) and three forms: D. capensis ‘Alba’ (Fig. 2), D. capensis ‘Narrow Leaf’
(Fig. 3) and D. capensis ‘Rubra’ (Fig. 4), coming from the collections of the Botanical
Gardens ”Alexandru Borza” of Cluj-Napoca, has been fixed and preserved in 70% ethylic
alcohol. The sections were cut by microtome, coloured with iodine green and alauncarmine, mounted in gel and analyzed in a Novex (Holland) light microscope. The light
micrographs were performed by means of the same light microscope, using Canon A95
camera.
Results and discussions
The root (Fig. 5-7)
*
‘Anastasie Fătu’ Botanical Garden, ‘Al. I. Cuza’ University, [email protected]
Faculty of Biology, ‘Al. I. Cuza’ University, [email protected]
**
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The root in all analyzed species presents a primary structure. In Drosera capensis
and D. capensis L. ‘Narrow Leaf’, the rhizodermis, the exodermis and most of the cortical
parenchyma are exfoliated. In the other analyzed species, the rhizodermis present root hairs,
the exodermis is not organized and the cortical parenchyma is quite thin (3-7 rows of
amiliferous cells). All species have a secondary type endodermis, with uniform, but
moderately-thickened and suberized walls, excepting the cells which check the diffusion of
water from xylem to cortex and show only thin, cellulosed walls. .
The central cylinder shows a poliarchic type structure, with numerous dispersed
phloemic bundles; the xylem vessels, solitary or grouped, present thickened and weak
lignified walls; they are also dispersed in the central cylinder and separated by the cells of
the cellulosed parenchyma, rich in starch grains.
The rhizome (Figs. 8-12)
The epidermis of the rhizome consists of cells with thick external wall and sessile
secretory trichomes. The rhizome evidences a thick amiliferous cortex, a secondary type
endodermis, consisting of cells with thickened and suberized walls. The central cylinder is
very thick and exhibits numerous vascular bundles disorderly dispersed in the fundamental
parenchyma, most of them presenting a leptocentric structure. The xylem vessels have thick
but weak lignified walls, while the phloem consists of sieved tubes and guard cells. Foliar
vascular bundles are present in D. capensis ‘Rubra’ (Fig. 12).
The aerial stem (Fig. 13-20)
In front side view, the epidermis presents cells with straight lateral walls. Stomata,
sessile secretory trichomes, stalked secretory trichomes (except D. capensis ‘Narrow Leaf’)
are present. Only D. capensis ‘Alba’ shows long protective hairs consisting of elongated
cells disposed on two parallel rows.
In all analyzed species, the cross section reveals a primary structure. The epidermis
consists of isodiametric cells of various dimensions. Stomata are prominent above the
surroundings cells; sessile (Fig. 15) and stalked (Fig. 16) secretory trichomes are also
present.
The cortex is chlorenchymatic, formed of three layers of cells with thin, cellulosed
walls. The central cylinder shows a sclerenchymatic sheath consisting of 7-8 layers of cells
with thickened and lignified walls. The fundamental parenchyma evidences 5 (6 in D.
capensis ‘Rubra’, 7 in D. capensis ‘Alba’) vascular bundles (Figs. 17-19). The xylem
vessels, with thin, but lignified walls, form an arc which surrounds the phloem and come
into contact completely (D. capensis ‘Alba’) or not (D. capensis ‘Rubra’, D. capensis
‘Narrow Leaf’) with the sclerenchymatic sheath. The phloem consists of sieved tubes and
guard cells. The pith is parenchymatic-cellulosed, of meatic type (Fig. 20), bearing big
polygonal cells with very thin walls.
The leaf
The leaf shows long petiole and long lamina. The mature tentacles contain a red
pigment, while in the young ones the pigment is not present or it is in a smaller quantity,
only in the glandular head, making them very attractive for the insects, together with the
shiny droplet. In D. capensis ‘Alba’ neither the mature tentacles nor the immature ones
present the red pigment in the glandular head that is why the form is called ‘Alba’.
The petiole (Figs. 21-27)
In all analyzed species, the cross section has a semicircular shape, with two adaxial
crests (Fig. 21), except D. capensis ‘Rubra’. The epidermis displays a great variety of
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elements: isodiametric cells; with the external wall of the cells covered by a thin cuticle,
anomocytic stomata, prominent above the surrounding cells, sessile (Fig. 24) and stalked
secretory trichomes. In D. capensis, only the sessile secretory trichomes are present. The
fundamental parenchyma consists of big, round cells, three adaxial vascular bundles (Fig.
25-27) and other two in the adaxial crests. The petiole of D. capensis ‘Rubra’ does not
present adaxial bundles. All of them consist of phloem (sieved tubes and guard cells) and
xylem (vessels with thickened, but weak lignified walls and xylemic parenchyma).
The foliar limb (Figs. 28-34)
In front side view, the epidermis shows polygonal cells, bearing waved lateral walls.
Stomata are present in both epidermis, so the limb is amfistimatic. The tentacles are present
in the adaxial face of the limb and on its edges, together with the sessile secretory
trichomes. The tentacles present on the center of the leaf are shorter than the others present
on the edges. If pray comes to the leaf, the longer tentacles curl towards the center of the
leaf, to cover the insect. At the same time, the entire leaf curls towards the prey.
All investigated species, except D. capensis ‘Rubra’, show stalked secretory
trichomes; the limb of D. capensis ‘Alba’ bears protective hairs, too.
The tentacles (Figs. 31-34) consist of stalked glands of complex structure; the gland
is egg-shaped and contains a red pigment which attracts the prey. The stalk bears tracheids
surrounded by parenchymatic cells. The glandular part bears numerous cells with twisted
thickenings, which communicate with the tracheids; the outer part of the tentacles’ head is
composed of 2-3 layers of glandular radial elongated cells (especially those from the
external layer) [3-5].
First of all, the gland secretes mucilage which catches the prey and enzymes which
degrade the small animal. Then, the resulted compounds of the digestion have to be
absorbed and used in the plant. This process is done by the tentacles, on one hand, and by
the sessile and stalked secretory trichomes, on the other hand. The latter trichomes help the
tentacles absorbing all resulted compounds and maintaining a clean leaf superficies.
The sessile secretory trichomes consist of a small number of cells. They show two
basal cells, two stalked cells and 2 (4) glandular cells. The stalked ones present
multicellular gland and a stalk of two layers of cells. The protective hairs consist of two
rows of elongated cells.
The cross section of the limb appears quite thin, just a little bit thicker toward the
middle vein. The mesophyll has a uniform structure, bearing round cells and 7 (7-9 in D.
capensis ‘Narrow Leaf’, D. capensis ‘Rubra’) vascular bundles (Fig. 30), with the same
structure as those of the petiole. The smaller bundles bear only a few phloemic elements.
Conclusions
In all investigated species, the root has a primary structure. The rhizodermis persists
or is exfoliated; the exodermis is not organized; the endodermis has secondary structure; the
central cylinder consists of xylemic and phloemic vascular bundles.
The rhizome has sessile secretory trichomes. All investigated species have thick,
amyliferous cortex, with secondary endodermis and several vascular bundles, collateraly
closed or leptocentric and a meatic parenchyma, the later consisting of large isodiametric
cells with slightly wavy walls.
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The aerial floriferous stem has a primary structure. The epidermis presents sessile
and stalked secretory trichomes. D. capensis ‘Alba’ shows, also, protective trichomes. The
central cylinder is surrounded by a peripheral sclerenchymatic sheath. The central cylinder
contains many vascular bundles.
The petiole is elliptic at all the studied species, rarely half-round in cross section.
The lamina is amphistomatic with anomocytic stomata. All the studied species have sessile
and stalked secretory trichomes or protective trichomes, as well as tentacles. All secretory
elements have various positions in the epidermis, various length, number of cells.
REFERENCES
1.
2.
3.
4.
5.
Juniper, B. E., Robins, R. J., Joel, D. M., 1989- The Carnivorous Plants. Academic Press, San Diego
Metcalfe C. R., Chalk L., 1972, Anatomy of the Dicotyledons. 1: 581-585, Clarendon Press, Oxford
Stănescu Irina, Toma C., 2008- Secretory structures of the carnivorous plants belonging to the Droseraceae
family. Proceedings of the 1st International Conference: Environment- Natural Science- food industry in
European Context, Baia Mare, 1: 323-326
Stănescu Irina, Gostin Irina, Toma C., 2008- Leaf structure considerations of some Drosera L. species. Acta
Horti Botanici Bucurestiensis, 33: 77-82
Irina Stănescu, Irina Toma, C. Toma, 2005- Considerations of the stem structure of some Drosera L. species.
Contribuţii Botanice, Cluj-Napoca, 40: 215-220
Explanation of plates
Fig. 1: Drosera capensis
Fig. 2: Drosera capensis ‘Alba’
Fig. 3: Drosera capensis ‘Narrow Leaf’
Fig. 4: Drosera capensis ‘Rubra’
Cross section of the root.
Fig. 5: Drosera capensis
Fig. 6: Drosera capensis ‘Alba’,
Fig. 7: Drosera capensis ‘Rubra’
Cross section of the rhizome.
Fig. 8: Drosera capensis
Fig. 9: Drosera capensis ‘Alba’
Fig. 10: Drosera capensis ‘Narrow Leaf’
Fig. 11-12: Drosera capensis ‘Rubra’
Cross section of the aerial stem.
Fig. 13, 15, 16, 17, 20: Drosera capensis
Fig. 14, 19: Drosera capensis ‘Narrow Leaf’
Fig. 18: Drosera capensis ‘Alba’
Cross section of the petiole.
Fig.: 21, 25: Drosera capensis ‘Alba’
Fig. 22, 23, 24: Drosera capensis
Fig. 26: Drosera capensis ‘Narrow Leaf’
Fig. 27: Drosera capensis ‘Rubra’.
Cross section of the foliar limb.
Fig. 28, 31 (tentacle): Drosera capensis L.
Fig. 29, 33 (tentacle): Drosera capensis ‘Narrow Leaf’.
Fig. 30, 32 (tentacle): Drosera capensis ‘Alba’.
Fig. 34 (tentacle): Drosera capensis ‘Rubra’
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IRINA STĂNESCU, C. TOMA
PLATE I
Fig. 1
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IRINA STĂNESCU, C. TOMA
PLATE II
Fig. 7
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IRINA STĂNESCU, C. TOMA
PLATE III
Fig. 13
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IRINA STĂNESCU, C. TOMA
PLATE IV
Fig. 19
Fig. 20
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Fig. 24
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IRINA STĂNESCU, C. TOMA
PLATE V
Fig. 25
Fig.26
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IRINA STĂNESCU, C. TOMA
PLATE VI
Fig. 31
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