DISTRIBUTION AND SYSTEMATICS OF THE FRESH-WATER RED ALGAL FAMILY THOREACEAE IN NORTH-AMERICA

North American populations and type specimens of Thorea and Nemalionop sis were compared using multivariate morphometrics and image analysis. We continue to recognise the separation of the two genera based on sp ore-bearing branch-to-assimilatory filament length ratio and assimilat ory filament density (less-than-or-equal-to 0.3 and loose for Thorea a nd greater-than-or-equal-to 0.6 and compressed for Nemalionopsis, resp ectively). Four species of Thorea were distinguished worldwide: T hisp ida (syn. T andina, T lehmannii, T ramosissima), T violacea (syn. T. b ackmannii, T. brodensis, T. gaudichaudii, T. okadae, T. prowsei and T riekei), T clavata and T zollingeri. The former two species have varia ble branched, non-clavate assimilatory filaments, whereas the latter t wo have unbranched, clavate assimilatory filaments. Thorea hispida has copious secondary branches while T violacea is sparsely branched. Tho rea clavata is differentiated from T. zollingeri by having fewer monos porangia 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. shawi i with long assimilatory filaments composed of barrel-shaped cells and N. tortuosa (syn. N. shawii f. caroliniana) with short assimilatory f ilaments having cylindrical cells. Only N. tortuosa has been collected on the continent, from Florida, Louisiana, and North Carolina.