Lichens are the "dynamic duo" of the plant world. They consist of a fungus and a photosynthetic partner (green algae or cyanobacteria, or sometimes both) that live and grow so intimately interconnected that they appear to be a single organism. The fungus surrounds its green partner and shares in the sugars and other carbohydrates that the alga or cyanobacterium produces by photosynthesis. At the same time the fungus provides a protected environment for its food-producing partner and expands its potential habitats. Lichen fungi have a range of nutritional relationships with their associated algae or cyanobacteria from almost pure parasitism to a very benign association called symbiosis, or, more specifically, mutualistic symbiosis, wherein both partners benefit equally from the partnership. Lichens are an extremely successful life form, with thousands of species throughout the world. Some are extremely tiny and inconspicuous, little more than a black or gray smudge, but...