Morphological Examination and Phylogenetic Analyses of Phycopeltis spp. (Trentepohliales, Ulvophyceae) from Tropical China

During an investigation of Trentepohliales (Ulvophyceae) from tropical areas in China, four species of the genus Phycopeltis were identified: Phycopeltis aurea, P. epiphyton, P. flabellata and P. prostrata. The morphological characteristics of both young and adult thalli were observed and compared. Three species (P. flabellata, P. aurea and P. epiphyton) shared a symmetrical development with dichotomously branching vegetative cells during early stages; conversely, P. prostrata had dishevelled filaments with no dichotomously branching filaments and no symmetrical development. The adult thalli of the former three species shared common morphological characteristics, such as equally dichotomous filaments, absence of erect hair and gametangia formed in prostate vegetative filaments. Phylogenetic analyses based on SSU and ITS rDNA sequences showed that the three morphologically similar species were in a clade that was sister to a clade containing T. umbrina and T. abietina, thus confirming morphological monophyly. Conversely, Phycopeltis prostrata, a species with erect filaments, sessile gametangia on the basal erect hair, larger length/width ratio of vegetative cells and very loosely coalescent prostrate filaments, branched separately from the core Phycopeltis group and the T. umbrina and T. abietina clade. Based on morphological and molecular evidence, the genus Phycopeltis was paraphyletic. Furthermore, the traditional taxonomic criteria for Phycopeltis must be reassessed based on phylogeny using more species. A new circumscription of the Phycopeltis and the erection of new genera are recommended.