Phylogenetic species delimitation in Pinnularia subgibba group and its congruence with morphology

Pinnularia Ehrenberg (1843) represents one of the most species-rich genus of freshwater diatoms (Bacillariophyceae). In this study, evolutionary distances between Pinnularia sequences of five molecular markers were compared. Nuclear marker 28S rDNA and mitochondrial COX1 have been found to be the most variable and therefore possess the greatest potential to distinguish between closely related species of the genus. These two markers were used to infer phylogeny and to suggest primary hypothesis on species limits within Pinnularia subgibba group represented by 59 strains. Total of 15 monophyletic species was delimited using three methods (SPNA, GMYC, PTP). Moreover, congruence of primary hypothesis with morphology was evaluated and other available lines of evidence (e.g. biogeography, reproductive compatibility) were taken in consideration. To summarize, results suggest that several clades of Pinnularia subgibba group represent morphologically distinct species which might be unknown to science. Others can be relativelly clearly associated with decribed taxa. Most of the clades, however, seem to be part of large polyphyletic gibba-subgibba-parvulissima species complex and it must be investigated in much more detail before coming to reliable conclusion on their true biological identity.