Phylogeny and Taxonomy of Xanthophyceae (Stramenopiles, Chromalveolata)

The stramenopile class Xanthophyceae has been variously divided into two to seven orders. Previous molecular phylogenetic analyses of the class have had limited taxon/gene sampling or have focused on particular taxa. Despite these limitations para-polyphyletic groups have been identified at different taxonomic ranks. To investigate the phylogeny of the Xanthophyceae, a multiple alignment containing SSU rDNA, rbcL and psaA gene portions was analyzed according to bayesian inference, maximum likelihood, minimum evolution and maximum parsimony methods. This multigenic approach allowed robust resolution of evolutionary relationships within Xanthophyceae and the proposal of a taxonomic revision within the class. The best statistically supported tree either showed/or confirmed that several taxa at different taxonomic levels were para-polyphyletic. Ten epitypes were formally proposed for species of Chlorellidium, Botrydiopsis and Bumilleriopsis. Boundaries of these coccoid genera were redefined as monophyletic groups. Four major clades received strong statistical support. These accommodated most of the studied coccoid, filamentous and siphonous Xanthophyceae. Unicellular flagellates, amoeboid and palmelloid taxa were not included in the study. Botrydiopsis pyrenoidosa was excluded from Xanthophyceae and placed incertae sedis.