Lichen
20% (one in five) of fungal species live in lichens. Lichen fungi belong to several different groups of fungi. Most common (over 40%) are Ascomycetes, which produce spores in a sac-shaped container, the ascus. Only a few types of alga occur within lichens; these algae also have their own names. Algae may be sometimes the dominant partner in so-called 'jelly lichens', Collema and Leptogium, but this is rare. More usually, the algae are the green alga Trebouxia. Other species are the orange Trentepohli, and the cyanobacterium Nostoc.p9–10