Date of Award




First Advisor

Dr. Jeffrey Johansen


This study was conducted to determine the taxonomic placement of falsely-branched taxa in the soil crusts of San Nicolas Island, which is the largest of the Channel Islands lying off the coast of California. After microscopic analysis of the strains collected from the island, a phylogenetic analysis of 16S rRNA genes, and an analysis of the 16S-23S ITS region, we have identified that these strains belong to the soil genus Spirirestis, which is in the Tolypothrichaceae family. The Tolypothrichaceae is a wellcharacterized monophyletic lineage of non-attenuated, false-branching heteropolar types containing the genera Spirirestis, Hassallia, Tolypothrix, Coleodesmium, and Rexia. The strains analyzed specifically belonged to the genus Spirirestis, which is characterized by having heterocyte formation, false branching, presence of sheath, and tightly spiraled trichomes. In addition to determining the taxonomic placement of the falsely- branched taxa in the soils of San Nicolas Island, we reassessed the Tolypothichaceae family. Based on our results, there was a clear distinction between the soil and the aquatic clades in the family. However, the family should not be split into two families due to high similarity of the 16S rRNA genes. The Tolypothrichaceae needs revision based on the presence of many polyphyletic genera.

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