Phylogenetic relationships within the stylonematales (Stylonematophyceae, Rhodophyta):: Biogeographic patterns do not apply to Stylonema alsidii

The Stylonematales is the sole order of the Stylonematophyceae. The order consists of a mixture of filamentous or unicellular taxa that are small, grow on various surfaces, and are described from many floras, indicating that they may be cosmopolitan. Such ubiquity has been proposed to be due to properties of microorganisms, such as large population sizes, rather than human-derived phenomena. While their small nature makes most records fortuitous, we targeted these red algae to get a better understanding of their global distribution, genetic variation, and phylogeographic relationships. Our results indicated that the genera are mostly well supported, except for the position of Stylonema cornu-cervi with Goniotrichopsis reniformis, while intergeneric relationships are mostly unsupported. The most commonly isolated species was Stylonema alsidii. Within this species, several well-supported clades were present. The phylogeographic relationships in S. alsidii showed no obvious biogeographic pattern, with supported clades containing samples from disparate locations, and multiple samples from the same area not grouping together. Some clades showed little genetic variation and wide distributions, possibly indicating human-derived dispersal. Other clades, also with wide distribution, showed more genetic structure and could be candidates for groups formed by natural long-distance dispersal. While all issues on ubiquity cannot be answered with this data set, it would appear that at least S. alsidii is a true ubiquitous taxon. The sister relationship of Rufusia pilicola to the remaining Stylonematophyceae, the presence of the carbohydrate floridoside, and this species' unusual habitat indicate that it belongs to a new order, Rufusiales.