Background – Micrasterias fimbriata, a conspicuous desmid species, has recently been shown to be composed of two clearly delimited monophyletic clades within the genus Micrasterias, closely related to several other well-defined Micrasterias species
(M. brachyptera, M. rotata, M. torreyi). The members of both clades can also be unambiguously recognized by careful morphological analysis. In addition, their distribution areas in Europe and North America are largely vicariant. Interestingly, morphological features of one of
the clades do not correspond with any of the previously described infraspecific taxa of M. fimbriata.
Material and methods – The study was based on a combination of morphological and molecular phylogenetic analyses of the clonal strains and natural populations.
Key results and conclusions – In this study, we present formal taxonomic description of Micrasterias compereana for specimens formerly included within traditional M. fimbriata, but differring in their phylogenetic position and discriminative morphological characteristics.
Phylogenetic analysis was based on the nuclear 18S rDNA and the plastid-encoded trnGUCC
intron sequence data. Morphological differences between species were illustrated by light and scanning electron microscopy. The analysis of natural samples, strains and published records
showed that M. compereana occurs in North America and western Europe. Conversely, M. fimbriata sensu stricto probably only occurs in temperate and boreal regions of Europe and Asia.