An overview of the Drepanocladus sendtneri complex

Abstract

The Drepanocladus sendtneri (Schimp. ex H. Müll.) Warnst. complex is revised. Due to much overlap in characters traditionally used to separate taxa within this complex, characters that have not been used in this group before are evaluated. Four species are recognised, Drepanocladus sordidus (C. Müll.) Hedenas, (Hypnum sordidum C. Müll.; syn. D. tenuinervis T. Kop.), occurring in Eurasia and the Americas, D. sendtneri, known from Eurasia and southern Africa, D. brachiatus (Mitt.) Dix., an Australian-New Zealand endemic, and D. latinervis Warnst., known from the arctic parts of Asia and North America. Drepanocladus brachiatus differs from the other three species in being autoicous rather than dioicous, and by always having a relatively low nerve width/leaf length ratio. In addition, it differs from D. sordidus and D. sendtneri in having a 3(−4)-stratose rather than (3−)4–5(−6) stratose nerve. Drepanocladus latinervis differs from the other species by its high median leaf lamina cell length (μm)/leaf length (mm) ratio (37.6–45.6), and the five specimens seen so far were all small (stem leaves 1.1–2.2 mm long). Drepanocladus sordidus and D. sendtneri are the two species most similar to each other. In D. sordidus, the ratio between the median leaf lamina cell length (μm) and the leaf length (mm) has values between 23.3–36.5, and the ratio between median leaf lamina cell width (μm) and leaf length (mm) has values between 1.9–5.9. In D. sendtneri the corresponding values are 17.9–24.4 and 1.5–4.2, respectively. Drepanocladus sendtneri is a species of strongly calcareous wetland habitats, that in some cases dry out temporarily during dry periods, whereas D. sordidus occurs in less mineral-rich wetland habitats, such as mesotrophic fens, or submerged in mesotrophic lakes. The habitats of D. brachiatus and D. latinervis are insufficiently known.