Abstract
Lichens are fungi with a specialized nutritional mode involving algae, or cyanobacteria, or both. Classification is based on the fungal partner, and around 13 500 species are known. The association is ancient, and the first ascomycete fungi with fruit bodies may have been lichenized. Adaptations to tropical habitats include extensive utilization of trentepohlioid algae, the production of large multi-celled spores capable of forming numerous germ tubes, and water-repellant hydophobins coating internal cell walls. Many tropical groups lack modern monographs and numerous new species are discovered in detailed studies. Lichens merit more attention in the tropics as bioindicators of habitat disturbance.
Highlights
Lichens are fungi with a specialized nutritional mode involving algae, or cyanobacteria, or both
Not a systematic, group consisting of fungi which have developed a specialised nutritional mode by combining with green algae and/or cyanobacteria to obtain their carbohydrates, and forming a structure in which the fungal tissues envelop their photosynthetic partners (Hawksworth 1988)
About one-fifth of all known extant fungal species form obligate mutualistic symbiotic associations with green algae, cyanobacteria or both photobionts, amounting to c. 13 500 fungal species (Sipman & Aptroot 2001), and these combine with c. 25 genera of algae and 15 genera of cyanobacteria (Honegger 2001)
Summary
Not a systematic, group consisting of fungi which have developed a specialised nutritional mode by combining with green algae and/or cyanobacteria to obtain their carbohydrates, and forming a structure in which the fungal tissues envelop their photosynthetic partners (Hawksworth 1988). They can be interpreted as independent ecosystems rather than organisms (Farrar 1976). The dual organism per se, that we call a lichen, strictly still has no independent name (Hawksworth 1997), and lichens are classified in the general fungal system according to the nature of the fungal partner.
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