Desmodesmus baconii (Chlorophyta), a new species with double rows of arcuate spines.

A new species of the chlorophycean genus Desmodesmus, D. baconii, was described based upon analyses of the morphology of the coenobia and DNA sequences from the nuclear ribosomal 18S RNA gene and the internal transcribed spacer region. Desmodesmus baconii was unusual in that it possessed two rows of spines only on the terminal cells. This species was easily distinguished from other Desmodesmus taxa with two rows of spines by the point symmetry of the coenobia and the lack of rows of spines on median cells of four-celled coenobia. Spines tapered from prominent incurved spines near one pole to small spines at the opposite pole. Median cells and the pole of terminal cells opposite the large spines had two or three short spines. Cell sizes were slightly larger for two-celled (4.2-6.7 μm × 1.6-2.9 μrn) than for four-celled coenobia (3.2-6.5 μm × 1.2-4.5 μm). Results of analyses of DNA sequence data indicated that D. baconii, although a member of the monophyletic genus Desmodesmus, was not closely allied with any other Desmodesmus taxon. Desmodesmus baconii was isolated from hypereutrophic Lake Chicot in Arkansas, USA, and is not known from any other location [ABSTRACT FROM AUTHOR]