Distribution and systematics of the freshwater red algal family Thoreaceae in North America

Abstract

North American populations and type specimens of Thorea and Nemalionopsis were compared using multivariate morphometrics and image analysis. We continue to recognise the separation of the two genera based on spore-bearing branch-to-assimilatory filament length ratio and assimilatory filament density (≤0·3 and loose for Thorea and ≥0·6 and compressed for Nemalionopsis, respectively). Four species of Thorea were distinguished worldwide: T. hispida (syn. T. andina, T. lehmannii, T. ramosissima), T. violacea (syn. T. bachmannii, T. brodensis, T. gaudichaudii, T. okadae, T. prowsei and T. riekei), T. clavata and T. zollingeri. The former two species have variable branched, non-clavate assimilatory filaments, whereas the latter two have unbranched, clavate assimilatory filaments. Thorea hispida has copious secondary branches while T. violacea is sparsely branched. Thorea clavata is differentiated from T. zollingeri by having fewer monosporangia per cluster. Two of these species were found in North America: T. hispida in Mexico, Grenada and Jamaica, and T. violacea in Texas and Mexico. Two species of Nemalionopsis were differentiated: N. shawii with long assimilatory filaments composed of barrel-shaped cells and n. tortuosa (syn. N. shawii f. caroliniana) with short assimilatory filaments having cylindrical cells. Only N. tortuosa has been collected on the continent, from Florida, Louisiana and North Carolina.