The symbiotic association between algae and fungi is called lichens. The algal partner is called Phycobiont and the fungal partner is called Mycobiont. Algae provide nutrition for fungal partner and also help in fixing the thallus to the substratum through rhizinae. Asexual reproduction takes place through fragmentation, Soredia and Isidia. Phycobionst reproduce by akinetes, hormogonia, aplanospore, etc. Mycobionts undergo sexual reproduction and produce ascocarps.
Classification:
1. Based on the habitat lichens are classified into following types: Corticolous (on bark) Lignicolous (on wood) Saxicolous (on rocks) Terricolous (on ground) Marine (on siliceous rocks of sea) and Fresh water (on siliceous rock of fresh water).
2. On the basis of morphology of the thallus they are divided into Leprose (a distinct fungal layer is absent) Crustose – crust like; Foliose – leaf like; Fruticose – branched pendulous shrub like.
3. The distribution of algal cells distinguishes lichens into two forms namely Homoiomerous (Algal cells evenly distributed in the thallus) and Fleteromerous (a distinct layer of algae and fungi present)
4. If the fungal partner of lichen belongs to ascomycetes, it is called Ascolichen and if it is basidiomycetes it is called Basidiolichen.
