LAUSR

The freshwater red algal order Thoreales has triphasic life history composed of a diminutive diploid “Chantransia” stage, a distinctive macroscopic gametophyte with multi‐axial growth and carposporophytes that develop on the gametophyte thallus. This order is comprised of two genera, Thorea and Nemalionopsis. Thorea has been widely reported with numerous species, whereas Nemalionopsis has been more rarely observed with only a few species described. DNA sequences from three loci (rbcL, cox1, and LSU) were used to examine the phylogenetic affinity of specimens collected from geographically distant locations including North America, South America, Europe, Pacific Islands, Southeast Asia, China, and India. Sixteen species of Thorea and two species of Nemalionopsis were recognized. Morphological observations confirmed the distinctness of the two genera and also provided some characters to distinguish species. However, many of the collections were in “Chantransia” stage rather than gametophyte stage, meaning that key diagnostic morphological characters were unavailable. Three new species are proposed primarily based on the DNA sequence data generated in this study, Thorea kokosinga‐pueschelii, T. mauitukitukii, and T. quisqueyana. In addition to these newly described species, one DNA sequence from GenBank was not closely associated with other Thorea clades and may represent further diversity in the genus. Two species in Nemalionopsis are recognized, N. shawii and N. parkeri nom. et stat. nov. Thorea harbors more diversity than had been recognized by morphological data alone. Distribution data indicated that Nemalionopsis is common in the Pacific region, whereas Thorea is more globally distributed. Most species of Thorea have a regional distribution, but Thorea hispida appears to be cosmopolitan.