Lichens are symbiotic organisms composed of both an alga and a fungus. They dominate approximately 8% of terrestrial ecosystems and are important contributors to mineral cycling in many areas. Also they are important biological indicators of pollution hazards such as sulfur dioxide. Dr. Thomas Nash of Arizona State University is studying the species of lichens of the genus Xanthoparmelia in South America, in order to determine reliable morphological and biochemical characters by which to recognize individual species and further to attempt to determine the evolutionary affinities of these taxa. Hundreds of novel chemical compounds (so called "lichen substances") have been identified in various lichens, and used at times as species markers. Dr. Nash will test whether these chemical types are stable features of particular species or whether the chemistry varies with environmental conditions under which the lichens grow. His taxonomic work on South American lichens will complement projects underway or completed on this genus for South Africa, Australasia, and North America, covering ultimately nearly 400 species.
