3. Introduction
Adiantum, the maidenhair fern is a genus of about 250 species of fern in the
subfamily vittarioideae of the family Pteridaceae, though some researchers place it
in its own family, Adiantaceae. The genus name comes from Greek, meaning
“unwetted”, referring to the fronds ability to shed water without becoming wet.
They generally prefer humus rich, moist, well-drained sites, ranging from
bottomland soils to vertical rock walls. Many species are especially known for
growing on rock walls around waterfalls and water seepage areas. The highest
species diversity is in the andes. Fairly high diversity also occurs in eastern asia,
with nearly 40 species in china.
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6. Characteristics
They are distinctive in appearance, with dark, often black stipes and rachises, and bright green, often delicately cut
leaf tissue.
The sori are borne submarginally, and are covered by reflexed flaps of leaf tissue which resemble indusia.
Dimorphism between sterile and fertile fronds is generally subtle.
Adiantum pedatum, fern which typically grow 1.5 to 2 tall and is most frequently found on rich wooded slopes, ravine
bottoms and damp shady woods.
Rhizome is a perennial, subterranean dichotomously branched structure and is creeping in A. capillus-veneris or may
be erect as in A. caudatum.
The roots are adventitious and arise from the rhizome.
The leaves are also called fronds and are pinnately compound the young leaves are circinately coiled.
The petiole is long, black and shiny.
The venation is free and dichotomous in all the species.
The vein spread in a fan-like manner in the lamina.
The leaves bear marginal sori which are covered by a false indusium.
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7. The rhizome in transverse section shows a single layered epidermis covered by cuticle.
Some epidermal cells bear multicellular hairs.
The Epidermis is followed by two to three layered hypodermis made up of sclerenchyma
tissue.
A parenchymatous ground tissue is present.
The young rhizomes have amphiphloic siphonostele.
The older rhizomes have solenostele or dictyostele .
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Internal structure
Root
The root is differentiated into epidermis, cortex and central vascular cylinder.
The epidermis is the outermost layer and bears unicellular root hairs.
The cortex is divided into outer wide parenchymatous and inner narrow
sclerenchymatous layer.
The stele is simple and possesses a central core of xylem in diarch condition with
phloem on either side of it .
Rhizome
8. Petiole
The petiole in T.S. shows a single layered epidermis with thick cuticle.
Epidermis is followed by a sclerenchymatous hypodermis which provides mechanical support.
There is an extensive parenchymatous ground tissue.
The central region possesses a single large horse shoe shaped stele.
Xylem forms central core surrounded by phloem.
Pinnule
The Pinnule shows upper and lower epidermis.
The cells contain chloroplasts.
Stomata are confined to lower epidermis.
The mesophyll is not differentiated into palisade and spongy parenchyma.
The vascular bundle is surrounded by sclerenchymatous bundle sheath.
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Reproduction
Adiantum is homosporous. The reproduction takes place by the production of spores. The spores are
produced in sporangia. A group of sporangia forms sori. The sori are marginal but the reflex margins of the
pinna form a protective membranous structure called false indusium . The development of sporangium is of
leptosporangiate type.
The sorus does not show any definite sequence hence fall under
mixed type. A mature sporangium bears a multicellular stalk and a
spherical or elliptical single layered structure called capsule. The
capsule contains haploid spores. The wall of the capsule is
differentiated into thick walled annulus and thin walled stomium.
On maturity the sporangium bursts and spores are released. The
spores germinate and undergo repeated division to produce
a prothallus. The prothallus is flat, green and heart shaped. It is
monoecious and represents the gametophytic phase. Sex organs
called antheridia and archegonia develop on the prothallus.
Antheridia release multiflagellate antherozoids which swim in
water and reach the egg of the archegonium to accomplish
fertilization.
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Species of Adiantum
Adiantum species:
A-B( A. pseudotinctum)
A. Frond.
B. Pinnules abaxially.
C.( A. pentadactylon)
Habit
D-F( A. sinuosum)
D. Habit.
E. Young plant.
F. Sori.
G-I( A. glaucescens)
G. Frond.
H. Pinnules abaxially.
I . Sori
