THE MOLECULAR PHYLOGENETIC AND GEOMETRIC MORPHOMETRIC EVALUATION OF MICRASTERIAS CRUX-MELITENSIS/M. RADIANS SPECIES COMPLEX1

We investigated nine strains of the Micrasterias crux-melitensis (Ehrenb.) Hassall ex Ralfs and M. radians W. B. Turner species complex. A combination of molecular, morphological, and geometric morphometric data was used to reveal the patterns of their phenotypic and phylogenetic differentiation. The molecular data based on internal transcribed spacer (ITS) rDNA, glycine transfer RNA (trnGuuc) intron, and SSU rDNA sequences revealed three phylogenetic lineages. One of them comprised the six European and North American strains that were morphologically identified as M. crux-melitensis. Phenotypic data illustrated high morphological variability of strains within this genetically homogenous lineage that spanned several traditional infraspecific taxa, including strains corresponding to M. crux-melitensis var. janeira (Racib.) Grönblad and M. crux-melitensis var. superflua W. B. Turner, whose morphometric characteristics profoundly differed. Three strains of M. radians formed two separate phylogenetic lineages corresponding to traditional varieties M. radians var. evoluta (W. B. Turner) Willi Krieg. and M. radians var. bogoriensis (C. J. Bernard) G. S. West. The morphological types corresponding to the former variety have, so far, only been reported from Africa. Therefore, we cannot preclude that geographic isolation may play a role in species differentiation of relatively large freshwater protists, such as Micrasterias.