ITS2 sequence-structure phylogeny in the Scenedesmaceae with special reference to Coelastrum (Chlorophyta, Chlorophyceae), including the new genera Comasiella and Pectinodesmus

Abstract

Hegewald E., Wolf M., Keller A., Friedl T. and Krienitz L. 2010. ITS2 sequence-structure phylogeny in the Scenedesmaceae with special reference on Coelastrum (Chlorophyta, Chlorophyceae). Phycologia 49: 325–335. DOI: 10.2216/09-61.1Sequences and secondary structures of the nuclear-encoded internal transcribed spacer 2 (ITS2) ribosomal RNA of nine Coelastrum taxa, Asterarcys quadricellulare (Coelastraceae), Westella botryoides (hitherto Oocystaceae) and Dimorphococcus lunatus (Scenedesmaceae) were determined and compared with existing GenBank entries of scenedesmacean taxa (Desmodesmus, Enallax, Neodesmus, Scenedesmus). Phylogenetic analyses showed that the studied Coelastrum taxa belong to several different lineages within the Scenedesmaceae: five Coelastrum taxa (Coelastrum microporum, Coelastrum astroideum, C. astroideum var. rugosum = Coelastrum rugosum, Coelastrum pseudomicroporum and Coelastrum sphaericum incl. Coelastrum proboscideum) form monophyletic clades, whereas two strains labeled Coelastrum morum belong to different genera. The African strain of C. morum clusters with Coelastrum cambricum. The Finnish strain labeled C. morum clusters with Asterarcys, Dimorphococcus and Hariotina. According to its morphology this strain belongs to Coelastrella, related to Coelastrella saiponensis. Westella botryoides belongs to a separate clade within the Scenedesmaceae. Coelastrum reticulatum is positioned in the clade with Asterarcys, Dimorphococcus and Coelastrella; hence its separation in a separate genus, as originally described (Hariotina), is justified. In general, the phylogenetic analysis of ITS2 data shows that the Coelastraceae are included in the monophyletic Scenedesmaceae, and thus the splitting into two families is not justified, but they belong to the monophyletic subfamily Coelastroidea. The genera Comasiella and Pectinodesmus are newly erected, and several new combinations are proposed.