Biodiversity of spirogyra and sirogonium in the Hawaiian Islands: molecular insights into two morphologically similar macroalgal genera

Abstract

Spirogyra is a filamentous green algal genus with >380 species found in freshwater systems worldwide. Despite its prevalence, there is much taxonomic confusion between Spirogyra and the closely related and morphologically similar genus, Sirogonium. DNA sequences of selected regions of cp23S rRNA (UPA), rbcL, and nu18S were obtained from 151 isolates of Spirogyra and putative relatives in the Hawaiian Islands. Individual and concatenated sequence data sets were analyzed using maximum parsimony, maximum likelihood and Bayesian inference. Morphological characters were also measured and analyzed for each collection, and compared to results based on sequence data. Twelve species of Spirogyra/Sirogonium were identified in the rbcL and UPA trees, and as in previously published analyses, Spirogyra and Sirogonium are paraphyletic. This first molecular phylogenetic study of relationships within Spirogyra/Sirogonium in the Hawaiian Islands contributes important data on variation among the most isolated of all Spirogyra populations in the world and thus the groundwork for a better understanding of these genera worldwide.