Problems of epitypification in morphologically simple green microalgae: a case study of two widespread species of Klebsormidium (Klebsormidiophyceae, Streptophyta).

The extensive genetic cryptic diversity revealed by molecular studies in many green microalgae has caused great uncertainties in the circumscription of some species described on strictly morphological grounds. These uncertainties should be resolved by obtaining molecular data from type materials, but this procedure is not feasible in many species because the type specimens are illustrations, or too small or poorly preserved to obtain DNA sequence data. In these situations, the selection of an epitype is often a mandatory requirement to define the identity of a species and establish unambiguously its position in molecular phylogenies. In this study we investigated the identity of two widespread species of Klebsormidium (Streptophyta), K. flaccidum and K. nitens, which were recently epitypified by Mikhailyuk and colleagues. We collected several specimens of these algae from the type localities and the original habitats of these two species, for which we examined morphology in the field material and in culture, and obtained sequences of the rbcL gene. On the basis of the original descriptions, we conclude that the designation of the epitype of K. flaccidum was correct, whereas the epitype of K. nitens (which consists of material collected tens of thousands of km from the type locality) was most probably incorrect. We discuss the implications of these decisions for the classification of Klebsormidium and, more generally, the importance of the correct choice of epitype material for the taxonomy of green microalgae.