The charophycean order Klebsormidiales consists of two unbranched filamentous lineages, the fresh water Entransia and the semiterrestrial Klebsormidium. Molecular data have supported the close relationship Klebsormidiales have with land plants. A monograph exists for the European species of Klebsormidium; this monograph provides a cladistic analysis of morphological characteristics for eight Klebsormidium species, but a species level molecular phylogenetic analysis has not yet been performed for the group. We have obtained fifty strains of Klebsormidium, representing eleven morphological species, both from nature and from culture collections. Phylogenetic analyses using rbcL, atpB, coxIII and nad5 gene sequence data from these strains and forty outgroup sequences suggest that several traditional Klebsormidium species may not be monophyletic.

Key words: algae, Charophycean, Klebsormidiales, Klebsormidium, systematics