Mojave National Preserve - Lichens

Lichens are among the hardiest organisms in the world, capable of growing in areas of extreme cold, heat, or drought. Over 500 unique biochemical compounds have been discovered from lichens, which help them to survive under harsh conditions. Under the proper conditions, lichens can colonize any undisturbed surface, including bare rock and desert sand. Lichens are quite common with over 3600 species described in the United States and Canada, but are quite commonly overlooked. Many lichens have very slow metabolisms and grow extremely slowly, and some are thought to be among the oldest living organisms on earth. Lichens are an important component of cryptobiotic soils, along with free-living cyanobacteria and mosses.

One of the most interesting aspects of lichens is that they are not a single organism but rather a symbiotic organism made up of as many as three distinct members. The dominant partner in this relationship is a fungus, most commonly of the order Ascomycotina. Fungi cannot produce their own food and usually function as decomposers, but the lichen fungi cultivate photosynthetic partners. Some of the partners are algae while others are cyanobacteria (blue-green algae). Some lichen fungi utilize both.

Lichens are quite diverse in terms of form and color, and are often categorized in terms of growth form and not in terms of relationships. There are three types of lichens, crustose, foliose, and fruticose. Crustose lichens form crusts which are tightly attached to the substrate. Foliose lichens have lobes which are leaf-like and are only loosely attached to the substrate. The lobes are generally parallel to the substrate. Fruticose lichens have a three-dimensional growth habit and may grow up like a shrub or hang down in strands.