A time-calibrated multi-gene phylogeny provides insights into the evolution, taxonomy and DNA barcoding of the Pinnularia gibba group (Bacillariophyta)

Many diatom groups are known for widespread (pseudo)cryptic species diversity and Pinnularia gibba group is one of them. Recently, Kollar et al. (2019) delimited species within the group by means of a polyphasic approach, providing an evidence for the existence of fifteen species. In order to further guide the systematic revision of the group, the present study focuses on the evolution and morphology of the P. gibba group. Using representatives of the fifteen species we used fossils to constrain and calibrate a multi-gene species-level phylogeny. Although many species are morphologically highly similar, significant differences in cell size were detected in different sections of the tree, suggestive of ongoing morphological differentiation. We further used the phylogenetic analysis to assess marker resolution for DNA barcoding, showing that the proposed diatom barcode markers rbcL and V4 SSU rDNA can distinguish closely related (pseudo)cryptic species of the group.