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The lichen genus Hypogymnia is widely distributed throughout the world, in such places as Europe, Asia, Africa, Australia, New Zealand, Japan, and North America. Currently, there are twenty-one recognized species of Hypogymnia in North America, but no comprehensive study of the genus in North America has been published. My study of the genus Hypogymnia was performed on a sample of 784 North American specimens collected from the western United States, southern Canada, the Great Lakes region, and the eastern United States. The morphological characteristics of each lichen specimen were examined. Chemical studies included preliminary spot test screening of the cortex and medulla of each lichen specimen, followed by thin layer chromatographic procedures to attempt to identify the lichen substances present in each specimen, and to evaluate the chemical variation within each species. In this preliminary study of the genus Hypogymnia in North America, specimens of fifteen of the twenty-one described species of Hypogymnia have been examined as well as specimens of four new, undescribed species tentatively recognized by Lawrence Pike (on loan from the u.s. National Herbarium at the Smithsonian Institution). Patterns of morphological variation and chemical variation were identified for each species. New chemical strains have been detected in Hypogymnia imshaugii. My examination of Pike's undescribed, new species leads me to support the recognition of three of the four species as valid species worthy of publication. Thus, I recognize a total of 24 species of Hypogymnia in North America north of Mexico. The first comprehensive key to all of these species of Hypogymnia has been prepared. Additionally a brief description of the morphology, chemistry and geographical distribution of each species is provided.



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