The mycobiont is mostly an Ascomycotina. The fungus is the dominant member of the partnership and determines the morphology of the lichen. Based on the chlorophyll content of alga, it was estimated that the alga Nostoc comprises about 5% of the lichen Peltigera. Beneath the algal layer is fungal medulla 400 to 1000 ^m thick. Electron microscopy shows that alga and fungus are in intimate contact but there is no penetration of algal cells by fungus. Lichen fungi are not specific to their algal components. Though experimental evidence is lacking, it is believed that mycobionts provide their algal partners with water and minerals and shield the algae from intense light.
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