First record of Dryopteris affinis s. str. (Dryopteridaceae, Pteridophyta) in North Rhine-Westphalia

Abstract

In Central Europe, five taxa of the Dryopteris affinis complex are now considered to be separate species, four of which occur in North Rhine-Westphalia. These include the triploid D. borreri, by far most common species, and two other triploid species, D. pseudodisjuncta and D. lacunosa. The latter has only recently been described as new, and is only known in NRW from a single locality. Using flow cytometry, a plant with suspiciously small spores, from the Schwalm-Nette district, was identified as the diploid D. affinis s. str. In contrast to our initial expectations that this species would be restricted to lowland sites on the atlantic fringe of the extreme northwest of NRW, it was subsequently detected repeatedly in the Süderbergland as well. Using flow cytometry, a number of records of D. borreri were also confirmed as well as new stations for tetra- and pentaploid hybrid plants (D. ×complexa and D. ×critica) arising by crossing with D. filix-mas. While localities with the pentaploid D. ×criti­ca have been known from NRW for quite a while, those of D. ×complexa represent the first records for this state. Three distribution maps, one for the unspecified D. affinis complex, one for the two species D. affinis s. str. and D. borreri, and one for the hybrids D. ×complexa and D. ×critica (as confirmed by cytology or flow cytometry), are presented to depict the North Rhine-Westphalian occurrence of these taxa. A combined map showing the plants’ distribution and the spatial pattern of annual precipitation reveals a restriction to areas receiving higher rainfall (usually more than 800 mm). This and additional ecological features suggest that the taxa of the D. affinis complex are more dependent on water supply than D. filix-mas. Generally, the taxa of the D. affinis complex are ferns found in woody habitats and prefer acidophilic beech forest communities, especially D. affinis s. str., however, is remarkably often found on secondary sites strongly influenced by man, like embankments of roads and ditches, sand pits, also on an artificial escarpment and in a quarry.