78 E. Lichens:As noted at the beginning of this exercise, fungi play an important role as symbionts with other organisms. The symbiosis of a fungus with an alga forms an organism known as a lichen. Generally, the fungal component of a lichen is usually a member of the Ascomycota (sometimes Basidiomycota) and the photosynthetic component is either Nostoc, a blue-green bacteria, or one of about six species of green algae. Lichens are widespread in nature, and able to inhabit areas where neither symbiont could survive as a separate entity. They can be found in the Arctic, in deserts, on alpine peaks. Lichens are economically important as pollution indicators, source of natural dyes, and food for animals. There are three common growth forms: a)crustose – forms a thin flat crust that is glued to the substrate. b)foliose – flat and leafy or round in outline; distinct upper and lower surface c)fruticose – basally attached strands with hair-like, or shrub-like growth form Identify the following lichens using the dichotomous key provided.
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