Lichens may belong to one, two, or all three of the following kingdoms: Fungi, Protista and Monera. Lichens are groups of multiple organisms, which may occur in the forms of fungi, protists and monerans. Although they share the classification of lichens, species vary widely in habitat, appearance and physical and biological characteristics depending on which kingdom they belong.
Lichens belonging to the kingdom Fungi have the ability to reproduce asexually and produce their own food through the process of photosynthesis. Fungal lichens may appear as mushrooms and other fungi on the outside, but contain lichen characteristics on the inside. Some lichen take the form of algae cells; these organisms belong to the kingdom Protista while other lichens are comprised of cyanobacteria and, as such, fall into the kingdom Monera. Monera lichen appear as blue-green algae, and live primarily in aquatic environments while protists may live on land or in the water, and fungal lichen typically grow on land. Lichen may grow in many habitats and tolerate extreme conditions, such as desert climates and the Arctic tundra, remarkably well. Lichens grow in soil and on decomposing plants and trees as well as rocks, tree leaves, tree bark and even other lichens. They reproduce sexually and asexually, and spawn from pores and seeds.