ANATOMICAL FEATURES OF THE VEGETATIVE ORGANS
OF SALVINIA NATANS (L.) ALL. (SALVINIACEAE)
CARACTERELE ANATOMICE ALE ORGANELOR VEGETATIVE
LA SALVINIA NATANS (L.) ALL. (SALVINIACEAE)
Rodica BERCU
Universitatea „Ovidius”, Constanţa, România
Abstract: The article comprises the investigation on
the structure vegetative organs of an aquatic fern,
namely Salvinia natans (L.) The specific fern
characters is represented, mostly, by the stem
structural organization, especially those of the
vascular system. The hydrophytic features such as
the presence of aerenchyma well developed in the
stem and submerged leaf and less in the emerged
leaf are described and discussed. Remarkable is the
heterogenous
mesophyll
with
numerous
chloroplasts and the blade epidermal papillae and
hairs.
Rezumat: Articolul conţine investigaţii asupra
structurii organelor vegetative ale unei ferigi
acvatice, Salvinia natans (L.). Caracteristicile
specifice ferigii sunt reprezentate, mai ales de
organizarea structurală a tulpinii, în special de cea
a structurii sistemului vascular. Trăsăturile
hidrofite cum ar fi prezenţa erenchimului bine
dezvoltat din tulpină şi frunzele submerse şi mai
puţin din frunzele aeriene sunt descrise şi discutate.
De remarcat mezofilul eterogen cu numeroase
cloroplaste şi papile şi peri epidermici
Key words: anatomy, stem, submerged dissected leaf, emerged leaf, Salvinia natans
Cuvinte cheie: anatomie, tulpină, frunză submersă disecată, frunză aeriană, Salvinia natans
.
INTRODUCTION
Salvina natans (L.) All., sometimes called floating water moss or simply salvinia, is
actually a floating aquatic fern. The stem is floating, filamentous and branched. The floating
leaves are longer than broad, 9-13-5-7 mm, entire at apex, arranged in regular rows and lying
flat on the water surface The leaves are small, round and covered with small hairs or papillae.
Papillae serve as water proofing. The plant consists of two floating leaves and a third
submerged dissected leaf that serves as a root. The spore cases are at the base of this
submerged leaf. Air cavities in the leaves help the tiny plant to stay afloat (Waterhouse and
Mitchell, 1998, Săvulescu, 1952.). An annual fern, in the wild this plant will grow very large
often covering entire lake surfaces. The species has been entered in the Red Data Book of
Ukraine (1996) and protected in the Danube delta (Ukraine and Romania). Reproduction by
spores and vegetatively. Information, however, on the anatomy of Salvinia natans (L.) All.
(vegetative organs), especially of the emerged and submerged leaves, is actually lacking.
MATERIAL AND METHODS
Cross sections of stems and leaves (emerged and submerged) were obtained using a
rotary microtome. The sections 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 DISCUSSIONS
Cross-section of the stem reveals a primary structure consisting of epidermis, cortex
and stele. The one-layered, slightly elongated, epidermis cells are thin-walled, covered by a
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thin cuticle and bear simple hairs. The cortex occupies the major portion of the petiole. It is
composed of an aerenchyma with large 7 air chambers separated by unicellular, unbranched
partitions (Grinţescu, 1985 Sporne, 1975), named trabeculae (Batanouny, 1992). (Fig. 1A, B).
The endodermis is composed of large thick-walled cells. Kroemer (1903) suggested that this
wall thickening was the result of cutinized blade superpositions, infirmed by other authors
(Ogura, 1938, Bierhorst, 1971, Bercu, 2004a) (Fig. 1C). The stele is represented by one-layered
pericycle and the vascular system embedded just in the centre of the aerenchymatic tissue. The
vascular system is poorly developed and consists of few centrally located xylem elements
(meta- and phloem vessels), surrounded by phloem. The protoxylem vessels interpenetrate the
phloem elements, constituted of sieve cells, lack companion cells and phloem parenchyma
forming a reduced protostele as Ogura (1938/72) reported with leptocentric trend (by our
opinion) (Fig. 1B).
a
b
Fig. 1. Cross sections of the stem. Portion with epidermis and cortex (a). A hair (b).
The stele (c): AC- air chamber, E- epidermis, Ed- endodermis, H- hair, Ph- phloem,
Pc- pericycle, St- stele, T- trabeculae, XV- xylem vessel (orig.).
The metamorphosed leaf. The third submerged dissected leaf serves as a root. Cross
section of the dissected leaf exhibits a single layer o epidermal cells, which are internally
connected to the cortex, the latter is composed of a ground tissue with large 6 air chambers
(aerenchyma), separated by trabeculae. The epidermal cells are thin-walled and slightly
irregularly radial-elongated, uncovered by cuticle and bear a number of secondary roots and
absorbent hairs. The centrally located stele is surrounded by 9 parenchyma cells. Beneath the
parenchyma cells is the pericycle and the vascular system (Fig. 2A, B). The xylem string is
located between the phloem bundles (two phloem bundles). That attributes to the root a diarch
structure. The diarch stele is composed of two xylem vessels fuse towards the centre. The 2
protoxylem vessels are exarch, facing the pericycle (Fig. 2C). The floating leaves, in
transversal sections, reveal a homogenous mesophyll. As other floating ferns (Azolla
filiculoides L.), the upper epidermis bears papillae and many-celled hairs (Andrews and Ellis,
1913; Bercu, 2004b), and consists of a single layer of cells, covered by a thin cuticle.
Remarkable are the grouped epidermal hairs which appear isolate towards the margins of the
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blade (Fig. 3A, B). Beneath the upper and lower epidermises is the mesophyll containing
numerous chloroplasts, differentiated into palisade and spongy tissue the latter with large air
spaces. The lower epidermis possesses smaller tipped hairs (Fig. 3C). Poorly developed
vascular elements are irregularly embedded the mesophyll, screened by the presence of
chloroplasts (Fig. 3A).
Fig. 2. Cross section of the dissected leaf. Portion with epidermis and cortex (a) A hair (b).
The stele (c): AC- air chamber, E- epidermis, Ed- endodermis, Ph- phloem, Pc- pericycle,
St- stele T- trabeculae, X- xylem (orig.).
The lower epidermal cells, in paradermal section, discloses undulated cells with
chloroplasts. Stomata are a screened, by the abundance of chloroplasts (Fig. 3D).
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Fig. 3. Cross section of the emerged leaf. Portions of the mesophyll with many-celled hairs (a, b). A lower
epidermal hair (c). Paradermal section (d): Cl- chloroplasts, EC- epidermal cell, H- hair, IS- intercellular
space, LE- lower epidermis, PT- palisade tissue, S- stoma, SP- spongy tissue, T- trabeculae, TH- tipped
hair, UE- upper epidermis (orig.).
CONCLUSIONS
Anatomically, Salvinia natans (L) All. exhibits characteristics of ferns with
hydrophytic features in accordance to its aquatic habit. The stem has a primary structure with a
conductive stele and a cortical aerenchyma. The dissected, submerged leaf cortex is also
aerenchymatic and is covered by an epidermis. The protostele consists of few xylem and
phloem elements. The emerged leaf has a chlorenchymatic heterogenous mesophyll placed
beneath the upper and lower epiderms. Large air cavities are present in the spongy tissue. The
upper epidermises bear many-celled hairs and the lower one, stomata, screened, such as the
vascular bundles, by the presence of chloroplasts.
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