Zwartsteel (Asplenium adiantum-nigrum L.) op de weg terug. Overzicht van het voorkomen in Nederland en de recentelijke uitbreidingen

In the Netherlands Asplenium adiantum-nigrum is a rare and severely threatened species. At the turn of the century the species showed a nearly continuous area in the southern part of the Province of Limburg, with one isolated outpost in the Province of Gelderland. The localities were mainly terrestrial. During the 20th century the species disappeared nearly totally from those localities. However, this loss of records has been compensated completely by a gradual extension on old walls, especially in the western parts of the Netherlands. This progress started in 1950, and increased ever since 1980. At present there are several vital populations in West-Netherlands. It is presumed that this increase is connected with the expansion of the taxon in its Eu-Atlantic area. Syntaxonomically the species is regarded as a transgressive character species of the Asplenietum ruto-murario-trichomanis. The combination of Bryum radiculosum and Asplenium adiantum-nigrum has been observed in the Netherlands for the first time.