Composition of lichen photobionts closely correlates with some taxonomic groups of lichen-forming fungi. More than 55% of these fungi are associated with Trebouxia Puym. and Asterochloris Tscherm.-Woess, around 40% with Cyanoprokaryota, about 8% with Trentepohliales, and 20% with other green algae. However, not all lichen associations are stable in long terms and therefore several photobiont species can be present in the same lichen thallus. Some lichens constantly include several photobiont species belonging to different taxonomic algal groups. Selectivity of various lichen groups is different because symbiotic relations of various lichens are situated on diverse specialization levels. Lichens with Trebouxia and Asterochloris reached the highest photobiont specificity levels. The origin of photobiont in lichen thallus and main ways of its obtainment in the process of lichen reproduction (from mother thallus (vegetative reproduction) and from environment (reproduction by spores)) are discussed. Lichen photobiont composition determines the main life strategies of lichen association as well as essentially influences on their eco-geographical peculiarities. Additional photobionts (in cephalodia) as well as hymenial (in hymenium) and epithecial (in epithecium) algae may be present in the thallus side by side with the main photobiont. Algae-lichenoepiphytes grown on lichen thalli, may penetrate into above mentioned lichen structures and perhaps serve source of “potential” photobionts.

Keywords: lichens, photobiont, mycobiont, symbiosis, coevolution, selectivity, parasitism, additional photobionts

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