Give a general account on lichens.

Explanation

1. The symbiotic association between algae and fungi is called lichens.
2. The algal partner is called phycobiont, and the fungal partner is called mycobiont.
3. Algae provide, nutrition for fungal partner and fix the thallus to the substratum through rhizinae.They reproduce by akinetes, aplanospore etc., Mycobionts produce ascocarps during sexual reproduction.
Classification :
1. Based on the habitat :
(i) Corticolous (on Bark)
(ii) Lignicolous (on Wood)
(iii) Saxicolous (on Rocks)
(iv) Terricolous (on Ground)
2. Based on morphology :
(i) Leprose (a distinct fungal layer is absent)
(ii) Crustose - Crust like
(iii) Foliose - Leaflike
(iv) Fruticose - Branched pendulous shrub like
3. Based on algal cells distribution :
(i) Homoiomerous - Algal cells evenly distributed in the thallus.
(ii) Heteromerous - Distinct layer of algae and fungi present.
4. Based on fungal partner:
(i) Ascolichen Fungal partner is a ascomycete.
(ii) Basidiolichen - Fungal partner is a schizomycetes. Economic importance :
1. Lichens secrete organic acids like Oxalic acids, helps in weathering of rocks, they act as pioneers in Xerosere.
2. Sensitive to air pollutants (sulphur-dioxide) and considered as pollution indicators.
3. Usnic acid produced from lichens show antibiotic properties.
4. Dye present in litmus paper (acid base indicator in labs) is got from Roccella montagnei.