Revision of the Genus Cryptomonas (Cryptophyceae) II: Incongruences between the Classical Morphospecies Concept and Molecular Phylogeny in Smaller Pyrenoid-less Cells

Previous studies have shown that the nuclear internal transcribed spacer 2 (ITS2) is likely a good marker to identify biological species according to its degree of conservation. Dimorphic strains and a few reports of sexual reproduction indicate the presence of biological species also in cryptophyte taxa. In this study, a reverse ( =  DNA-based) taxonomy approach was used to predict putative biological species in the genus Cryptomonas. Of 49 Cryptomonas strains, nuclear ITS2 and partial large subunit (LSU) rDNA sequences were used to determine groups of genetically identical strains. From each group, representative strains (a total of 30 strains) were chosen for improved molecular phylogenetic analyses with combined data sets (nuclear ITS2 and LSU rDNA and nucleomorph small subunit rDNA). To predict putative biological species in Cryptomonas, the secondary structures of the nuclear ITS2 sequences were compared among clades and among strains of the same clade. Mapping light microscopically visible...