De verspreiding en oecologie van Gymnocarpium dryopteris L. (Gebogen driehoeksvaren) in Nederland

Gymnocarpium dryopteris is rather rare in the Netherlands. Distribution and ecology have been surveyed, especially for the period 1979-1991. In this period the species was detected with more than 670 individual stands, 90% at the Kuinderbos. In this article the Kuinderbos population is compared with other Dutch populations. Gymnocarpium dryopteris prefers shadowy ditches, but may grow in various other habitats as well. Especially in the western and southern part of the Netherlands it is growing on walls. The vegetation on the sites belongs to different syntaxa, with a preference for the Quercion (Fago-Quercetum) or plantations (Pseudotsuga) and in the Kuinderbos especially plantations of Picea sitchensis. Gymnocarpium dryopteris is often accompanied by Athyrium filixfemina. Its rhizomes are creeping at 0.5-8 cm below surface, mostly in the ecto-organic layer, but along ditches also in the mineral layer. Most stands are within the influence of ground water. Usually individual stands are small, those with more than 1000 leaves are rare. Individual stands with more than 100 leaves are mostly fertile, with mostly less than 20% of the leaves bearing sori. On walls, small-sized individuals can be fertile as well.