COMMENTS ON LICHENS
Morphological structure of lichens
Asco-lichen
i) Crustose lichen:
The thallus of crustose lichen is poorly developed. It penetrates the substratums by the whole of its lower surface forming incrustations. It is partly or wholly embedded in the substratum. Superficially, it appears as an ashy and whitish crust marked by black, linear and curved fruiting bodies, apothecium. Eg: Graphis and Lecanora.
ii) Foliose lichen:
The thallus is flat, broad and much lobed with usually curled up irregular margins. it is dorsiventral with whitish or shooty lower surface that gives rise to central rhizoids- like strands called rhizinae for anchorage. The upper surface has a number of small cup-like fruiting bodies called apothecia. Eg. Physcia, Parmelia, etc.
iii) Fruticose lichen:
The thallus is complex, composed of slender cylindrical or flattened free bushy or erect or pendant branches The thallus shows us differentiation between upper and lower surfaces. It gets attached to the substratum by a strand of basal hyphae. Eg: Usnea, Cladonia, etc.
