Andreaea:-
1. Classification:-
Division:- Bryophyta
Class:- Bryopsida
Sub-class:- Andreidae
Order:- Andreales
Family:- Andreaceae
Genus:- Andreaea
2. Habit and habitat:-
> Andreaea is commonly known as “Granite moss” because it grows on siliceous mountain rock.
> It include 125 species.
> They grow in cold climate as arctic, antarctic, temperate and higher mountain altitudes of tropical zone.
> Most of the species occur in alpine or subalpine habitats in xeric substrates inhabiting exposed siliceous mountain rocks. But A. navalis grows on endocyte rocks submerged in the water of streams.
> In Sikkim (Eastern Himalayas) four species have been reported:
i. A. pterophylla
ii. A. densifolia
iii. A. rigida
iv. A. indica
> Connecting link:- It shares some features with Sphagnidae and some with Bryidae and thus form a connecting link between the two sub - classes.
3. Study of gametophyte:-
> Plant body is gametophytic and is of 1cm height.
> Dark brown to black or bluish green in colour and quite brittle.
> Large number of leaves are linear to lanceolate and spirally arranged.
> Rhizoids:-
- These are not uniseriate, multicellular, branched and oblique septate as in mosses, but are peculiar in structure.
- These are either cylindrical masses of cells or flattened cell plates which function as anchoring organs.
- Cylindrical masses are useful in penetrating the crevices of the hard rock.
- Flattened cell plates grows parallel for the purpose of absorption.
> Transverse section of stem is just like Sphagnum.
4. Reproduction by Gametophyte:-
Sexual reproduction:-
> Sex organs are grouped and terminal. This feature is resembles to true mosses.
> Structure and development of sex organs is similar to true mosses.
> Fertilization:-
- The process of fertilization is similar to other classes of bryophytes.
- Water is essential for fertilization.
- At the time of fertilization the neck canal cells along with the venter canal cell disintegrate to form a clear passage for the antherozoids.
- They enter through the cover cells and reach up to the egg, but only one fuses with the egg to form the zygote.
5. Study of sporophyte:-
> Archesporium develops from outer most layer of Endothecium.
> Capsule is almost cylindrical in shape.
> Seta is less developed like Sphagnum.
> Pseudopodium present like Sphagnum.
> Spore germinates and give rise a thalloid filamentous protonema.
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