Abstract
Light- and scanning electron microscopy are applied to re-assess diagnostic characters of type specimens and critical specimens of species in the genera Stemonitis and Symphytocarpus (Stemonitales, Myxomycetes) from the collections of the Natural History Museum London (BM). The results are used to discuss published data and the type status for specimens of Stemonitis ferruginea, S. flavogenita, S. herbatica, S. inconspicua, S. morganii, S. pallida, S. smithii, S. uvifera, S. virginiensis, S. webberi, Symphytocarpus amaurochaetoides, S. confluens, S. flaccidus and S. herbaticus. Due to severe shortcomings of the original description and the absence of preserved original material we regard S. axifera (Bull.) Macbride as a nomen ambiguum and propose to re-adopt the use of S. ferruginea as the valid name for the common taxon S. axifera auct. (non (Bull.) T.Macbr.). SEM characters support the treatment of Stemonitis smithii as a synonym of S. ferruginea. Stemonitis webberi instead is shown to be well separated from S. splendens by several independent characters. The importance of SEM characters for the correct identification of critical specimens of Stemonitis ferruginea, S.pallida and S. webberi is highlighted and accurate spore measurements based on SEM images are provided for all species.