The identity of the carbohydrate moving between the symbionts of a lichen depends on the genus of alga present. Twenty-seven lichen species, involving eight different genera of algae, have been examined. In lichens containing five genera of Chlorophyceae, carbohydrates move to the fungus as polyols (ribitol in Trebouxia, Myrmecia and Coccomyxa; erythritol in Trentepohlia; and sorbitol in Hyalococcus). In lichens containing three genera of Cyanophyceae (Nostoc, Calothrix and Scytonema) glucose was the carbohydrate moving, although there is a possibility that in the one lichen with Calothrix which was investigated, it may have been a glucan.
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