Nova Hedwigia, Beiheft 135, p. 201–237 February 2009 Taxonomy, ultrastructure and distribution of Gomphonemoid diatoms (Bacillariophyceae) from Great Smoky Mountains National Park (U.S.A.) E.W. Thomas 1,5 , J.P. Kociolek 2,3,5,6 , R.L. Lowe 1,2 and J.R. Johansen 4 1 Department of Biological Sciences, Bowling Green State University, Bowling Green, OH 43403 2 University of Michigan Biological Station, Pellston, MI 49769 3 Diatom Collection, California Academy of Sciences, 875 Howard Street, San Francisco, CA 94103 4 Department of Biological Sciences, John Carroll University, University Heights, OH 44118 5 Current address: University of Colorado, Museum of Natural History, University of Colorado, Boulder, CO 80305 6 Current address: Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80305 With 15 plates, 1 table and 1 appendix Abstract: The All Taxa Biodiversity Inventory (ATBI) of the Great Smoky Mountains National Park (GSMNP) is an ambitious effort to catalogue the entire biota of the park. As a part of this effort we are ex- amining diversity and microhabitat affinities of microalgae. The focus of this paper is to better understand the morphology and ultrastructure of the genera Gomphonema, Gomphoneis, and Gomphosphenia in the GSMNP, which have traditionally been confusing from a taxonomic point of view. Over 300 collections have been studied with light and scanning electron microscopy. Collections have come from all aquatic habitats in the park from streams to ponds to wet rock walls. In the present study a total of 30 species have been identified; 27 were members of the genus Gomphonema, 2 of the genus Gomphoneis and 1 species of the genus Gomphosphenia. Twenty percent of the taxa identified are new to science, including five species of Gomphonema and the one species of Gomphosphenia. The present list of taxa is compared to past reports for the Park, and the geographic distributions of the taxa considered. This survey provides for a better un- derstanding of species diversity of these genera, and offers insight into the possibility of finding new mem- bers of other genera in the Park and worldwide. Introduction The All Taxa Biodiversity Inventory (ATBI) has been pursuing the discovery of all species of life within the Great Smoky Mountains National Park (GSMNP) since 1997 (Pederson 1999, Shar- key 2001). As part of this work, a review and additions to our understanding of the algal flora of the Park has commenced. The focus of the current research is to examine members of the genera Gomphonema, Gomphoneis, and Gomphosphenia from habitats within the Park. These three genera span two families and occupy various habitats in GSMNP, ranging from ponds to rivers to subaerial rock faces. Some of the habitats contain multiple species from each genus, while others contain just one gomphonemoid species, and some habitats are completely lacking these taxa. Many North American Gomphonema have been confused and incorrectly identified (Koci- 1438-9134/09/0135-201 $ 9.25 © 2009 J. Cramer in der Gebrüder Borntraeger Verlagsbuchhandlung, D-70176 Stuttgart