Splitting of Micrasterias fimbriata (Desmidiales, Viridiplantae) into two monophyletic species and description of Micrasterias compereana sp. nov

The freshwater microalgal genus Micrasterias C.Agardh ex Ralfs represents a monophyletic lineage of the Desmidiaceae (Škaloud et al. 2011). Besides the species traditionally included in this genus on the basis of the morphological data (see e.g. Prescott et al. 1977, Růžička 1981, Coesel & Meesters 2007), the Micrasterias lineage also includes several morphologically dissimilar taxa, such as Micrasterias ralfsii (Brébisson ex Ralfs) Škaloud, Nemjová, Veselá, Černá & Neustupa and M. dickiei (Ralfs) Škaloud, Nemjová, Veselá, Černá & Neustupa. These species were previously classified into other desmid genera, but proved to be included within the phylogenetically defined genus Micrasterias on the basis of the multigenic molecular data (Gontcharov 2008, Hall et al. 2008, Gontcharov & Melkonian 2011, Škaloud et al. 2011). The morphological species concepts within the genus turned out to be relatively well supported by molecular data (Nemjová et al. 2011, Neustupa et al. 2010, 2011). While different populations of individual traditional species, such as M. rotata, typically formed monophyletic or closely related lineages (Neustupa et al. 2011), the phylogenetic species diversity of several other taxa, such as M. truncata Brébisson ex Ralfs, M. crux-melitensis Ralfs, or M. fimbriata Ralfs, proved to be higher than what was expected solely from the morphological data (Nemjová et al. 2011, Neustupa et al. 2010). The infraspecific phylogenetic clades of traditional M. crux-melitensis and M. truncata often could not be unambiguously delimited by morphological methods, and their separate species status remains uncertain. On the contrary, phylogenetic structure of the traditional M. fimbriata proved to be considerably less complicated (Neustupa et al. 2011). The natural populations and strains of this species, originating from various European and North American localities, turned out to belong to two well delimited and homogenous phylogenetic lineages on the basis of the group II intron sequences of the plastid encoded trnGUCC gene. Both lineages were firmly placed into the clade C of the genus Micrasterias sensu Škaloud et al. (2011). Interestingly, the members of the M. fimbriata lineages were clearly morphologically delimited and could be unambiguously recognized, either