Lichens are actually two organisms: a fungus and algae that form a symbiotic relationship and function very much like one organism. A common question about lichens is “Do they harm trees?” The answer is no. The algae part of the lichens is photosynthetic, and therefore they are able to produce their own energy and do not take any resources away from the trees. In fact, lichens often grow on nonliving substrates such as wood, concrete, tombstones, benches and so on.

The University of California Museum of Paleontology’s website describes lichen as, "... symbiotic associations of two different organisms..." The organisms referred to are fungus and algae. The protection and structural support offered by the fungus, and the food from photosynthesis by the algae, result in a working symbiotic relationship between the two. Lichens are commonly grayish-green, but may also be yellow or red, depending of the type of algae associated with the fungus.

With so many types of lichen, identifying the genus and species can be quite challenging. Experts have various ways to determine them. Naturalist Jim Conrad suggests that backyard gardeners recognize three types of lichen: Crustose, Foliose and Fruticose.. Crustose lichens look flat and white--like chalk drawn on the rocks--and grow on the rock like a crust. Foliose may appear similar in its young growth, but as it ages the edges curl up. Fruticose are shrub-like and, as the name suggests, resemble little shrubs. Possible Grasslands Species (Lichens of the Black Hills, Page 234) are Agrestia cyphellata, Lecanora lentigera – Restricted to gypsum soils, and  Parmelia chlorochroa.