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 characters of the 49 strains onto the phylogenetic trees revealed conflicts between classical morphospecies and putative biological species. Strains that were identical or almost identical in nuclear ITS2, showed cell shapes representing different morphological species, whereas strains seemingly belonging to the same morphological species were genetically too diverse to represent one biological species. Most of the five putative biological species could solely be identified by molecular signatures. Therefore, five species descriptions were emended by adding molecular signatures as diagnostic characters including a new combination, Cryptomonas commutata (Pascher) Hoef-Emden comb. nov.