Brief account and life cycle of Gleichenia
Gleichenia:-
1. Systematics:-
Division:- Pterophyta
Class:- Leptosporangiopsida
Order:- Gleicheniales
Family:- Gleicheniaceae (Forking Fern family)
Genus:- Gleichenia
2. Habit and Habitat:-
> Name Gleichenia, after German botanist Friedrich Wilhelm von Gleichen, 1717–1783.
> It is terrestrial, often growing in dense, open thickets.
> Gleichenia have a largely pantropical distribution.
> Gleichenia dicarpa, commonly known as pouched coral fern or tangle fern, is a small fern of the family Gleicheniaceae found in eastern Australia, New Caledonia and New Zealand. It forms tangled thickets in wet places such as swamps and riverbanks.
3. Study of sporophyte:-
> The stems are rhizomatous, the rhizomes creeping, dichotomously branched, with a “vitalized” protostele or rarely a solenostele.
> The leaves are often indeterminate in growth (sometimes reaching great lengths), with the rachises pseudodichotomously branched, 1-2-pinnate, veins free.
4. Reproduction:-
> Sori are round, abaxial, not marginal, exindusiate.
> Sporangia are round to pear-shaped, up to 5–15 sporangia per sorus, developing simultaneously, the annulus transverse-oblique.
> Spores are globose-tetrahedral or bilateral, trilete or monolete, 128–800 per sporangium.
> Gametophytes are large, green, surficial, with club-shaped hairs, developing endotrophic mycorrhizae.
> The mature gametophyte is cordate with wings which have a more or less irregular margin.
- As the thallus continues growth it becomes ribbon-like with a heavy midrib (10-18 cells thick) and uplifted ruffled wings.
- The base in large gametophytes is usually heavy and club-shaped.
- Old gametophytes may branch and maintain two apices producing archegonia.
- The rhizoids are stiff, abundant, usually reddish brown, and in general limited to the midrib.
- In many species two-celled glandular hairs develop on the midrib or wings in the region of the archegonia; the large tip cell may contain tannin.
- The hair arises from a special initial, a wedge-shaped cell cut off from the anterior side of a cell in the region of the archegonia. Occasionally such hairs are also found on the margin.
- The gametophytes are monoecious.
> Antheridia:-
- The antheridia vary greatly in size from relatively small to large and complex with 10-12 cells in the wall and with a spermatocyte content of several hundred.
- The cap cell is thrown off at dehiscence.
> Archegonia:-
- The archegonia have long necks directed towards the apex, ordinarily with seven to nine cells in a tier, but in Gleichenia vulcanica sometimes 12-14.
- The necks are approximately straight or bent forward towards the apex.
- The axial row usually consists of egg, ventral canal and a binucleate neck canal cell, but the presence of two canal cells in the neck is not unusual.