RECENT RADIATION OF THE PALMARIACEAE (RHODOPHYTA)

Molecular phylogenetic studies on the evolution of the red algae indic ate that this ancient division has many lineages that have recently un dergone radiations. One such example is the cold-temperate family Palm ariaceae. In this study, sequences from the ribosomal DNA internal tra nscribed spacer regions were compared among ten species in the Palmari aceae from both Atlantic and Pacific sites. Phylogenetic analyses of s equence data, in which Rhodophysema georgii Batters was used as outgro up and root, indicate a radiation into four clades, three of which con tain species of ''Palmaria'' and the fourth species of Halosaccion. Pa lmaria palmata (L.) Kuntze, the type and only North Atlantic species i n the genus, stands apart from all remaining species in the family and terminates the most basal branch in the rooted tree. The three more d erived clades have radiated mainly in the North Pacific. Southern Ocea n Palmaria and North Atlantic Devaleraea are hypothesized to have inva ded from separate but closely related North Pacific ancestors. The eas e with which sequences could be aligned combined with an unsaturated t ransition: transversion ratio and modest divergence involving predomin antly point mutations suggests that the initial radiation is relativel y recent (late Miocene-Pliocene) and that the Devaleraea-Palmaria clad e is even more recent (late Pliocene-Pleistocene).