Format: ORAL

Marcus Lehnert1,2,3, Tilo Monjau4, Christoph Rosche3,4

1 Herbarium (HAL), Martin-Luther-Universität Halle-Wittenberg, Neuwerk 21, 06108 Halle (Saale), Germany 2 Nees-Institut für Biodiversität der Pflanzen, Rheinische Friedrich-Wilhelms Universität, Meckenheimer Allee 170, D-53115 Bonn, Germany 3 German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Puschstr. 4, Leipzig 04103, Germany 4 Plant Ecology, Martin-Luther-Universität Halle-Wittenberg, Am Kirchtor 1, 06108 Halle (Saale), Germany

We present an overview of the morphology, biogeography and ecology of the fern genus Osmunda (i.e. without previously included taxa of Claytosmunda, Osmundastrum, and Plenasium), with a focus on the American O. spectabilis Willd. and Old World O. regalis L. While genetic data supports the separation of these taxa, commonly used morphologic characters to distinguish between O. regalis and O. spectabilis (maximum frond size; pinnae sessile vs. stalked; pinnules opposite vs. alternate; general pinnule proportions) are not infallible. We recorded morphometric differences among and between O. regalis and O. spectabilis and correlated these with spatio-environmental gradients. Our work provides an updated taxonomic overview with full synonymy and diagnostic key of Osmunda. We preliminarily recognize six informal subtaxa in O. regalis (“regalis”, “abyssinica”, “huegeliana”, “longifolia”, “transvaalensis”, “obtusifolia”) and three in O. spectabilis (“spectabilis”, “palustris”, “piresii”) which separate in a morphological traits-based PCA. The morphotaxa appeared geographically structured and their distribution showed significant correlations with elevation, mean annual precipitation, annual mean temperature and temperature seasonality. The taxonomic rank and validity of the proposed subtaxa has to be tested through a large-scale sampling, e.g. with comparative cp/nr genomic and cytogenetic analyses. Such future analyses may help to ascertain whether the observed morphologic peculiarities are conditioned solely by abiotic factors (which would allow addressing them as forms) or are manifested in the genome.