The recently described green algal genus Pseudorhizoclonium was erected for Rhizoclonium-like specimens that resolved as a separate clade from Rhizoclonium sensu stricto based on nuclear ribosomal DNA (SSU and LSU) data. We analysed 36 collections of Pseudorhizoclonium, including 18 new specimens, which resulted in a considerably extended distribution range that is mostly tropical to subtropical and includes Brazil, Madagascar, Philippines, French Polynesia, Panama, Tanzania, the Federated States of Micronesia, the Hawaiian Islands, Lord Howe Island (Australia) and temperate New Zealand. Ten distinct clades were resolved in phylogenetic analyses based on a combined SSU + LSU dataset, five of which were previously named as either Pseudorhizoclonium or Rhizoclonium species, and five of which likely represent novel lineages for this genus and are here named as new species (P. australe Boedeker, Leliaert & A.R.Sherwood, P. hawaiiense A.R.Sherwood, Boedeker & Leliaert, P. mangroviorum Boedeker, Leliaert & A.R.Sherwood, P. philippinense Leliaert, Boedeker & A.R.Sherwood, and P. subaerophilum A.R.Sherwood, Boedeker & Leliaert). Analysis of morphological characters demonstrated that although there was substantial overlap in character range for some lineages, others were distinct for one or more characters; however, morphological identification of the lineages is unreliable. The range of habitats in which these specimens were collected has been extended to include truly terrestrial areas and freshwater streams, which expands the known habitats of this genus beyond the original reports of mangroves, lagoons, and high intertidal areas. This genus represents an independent case of transition from marine into freshwater and terrestrial environments in the Cladophorales. Pseudorhizoclonium appears to have an unusually high tolerance for fluctuating environmental conditions, which may be related to the remarkable number of habitat transitions that have occurred within the genus. |
