Taxonomy, ultrastructure, and distribution of some gomphonemoid diatoms (Bacillariophyceae : Gomphonemataceae) from rivers in the United States

Using the continental-scale collections of the U.S. Geological Survey's Nat ional Water-Quality Assessment (NAWQA) Program, we examined selected member s of the family Gomphonemataceae to expand the current state of knowledge o f diatom taxonomy, morphology, and distribution. Ten taxa in the genera Gom phonema, Gomphoneis, and Gomphosphenia are examined. The taxonomic status o f two taxa is revised, and one new species is described. Two new features a re described for the genus Gomphonema: slit-like areolae and ridge-like fla ps or flanges on pseudosepta. Many North American gomphonemoid species appe ar to be restricted to certain geographic regions; the differences between western and eastern North America are striking. Trained analysts have had d ifficulty identifying and discriminating many of these taxa. We believe tha t this difficulty, in large part,results from our poor knowledge of the Nor th American flora. Large-scale monitoring programs such as NAWQA, when team ed up with research organizations withcommon interests, hold great promise to expand our knowledge of the biodiversity of North American ecosystems.