Morphology, molecular phylogeny, and species delimitation within microalgal genera Eubrownia, Spongiococcum, and Chlorococcum (Chlorophyceae, Chlorophyta)

Abstract

• Our knowledge of their taxonomic and phylogenetic relationships is still deficient. • Some genus and species from Moewusinia clade differ specific feature combinations. • The ITS2 of Eubrownia and Chlorococcum genera is unique within the chlorophytes. Despite that the diversity of chlorophycean microalgae has been studied for a long time, our knowledge of their taxonomic and phylogenetic relationships is still deficient. This study represents one of the first efforts to examine the congruence of the morphological identification of microalgal species from genera Eubrownia, Spongiococcum , and Chlorococcum with DNA-based species delimitation methods. We found unique combinations of morphological, molecular, and ecological features, distinguishing some members of the Moewusinia clade at the genus and species levels. Most genetic groups recovered by GMYC, ABGD, and PTP analyses of 18S rRNA and ITS2 were consistent with their morphological identification. The ITS2 region of genera Eubrownia and Chlorococcum is among the longest within the chlorophytes theretofore studied and has a unique secondary structure with branched helix III and uncommonly long helix IV. Moreover, the molecular signatures were found in the basal stem region of helix I, distinguishing two genera. The CBC analysis is able to effectively discriminate between E. isobilateralis, E. aggregata , and all Chlorococcum species, except for C. infusionum and C. echinozygotum . Thus, we confirmed tentative hypotheses of species, obtained by DNA-based delimitation methods, with morphological data, molecular signatures, ITS2 secondary structure, and CBC criterion.