Over het voorkomen van Teer guichelheil [Anagallis tenella (L.) Murray] op Texel

In the Netherlands Anagallis tenella occurs at the northeastern fringe of its area. Throughout the twentieth century the plant has declined in this country, and nowadays it is virtually restricted to the dune-areas of the islands of Texel and Voorne, its presence in other regions appearing either sinking or unstable. Its stations on Texel are described in some detail. The main vegetation types in which the species is found are reported in table 1. The Texel situation is compared with data on the (former) occurrence elsewhere in the Netherlands, as well as in adjacent countries. It turns out that – at least in the past – the plant was recorded in a surprisingly wide variety of habitats. These comprise young wet dune-slacks, borders of moorland and dune pools, fishponds, ditches and wet hay-fields in older dune-slacks, polders and brook valleys. In these habitats the plant could be found in vegetation types belonging to the phytosociological alliances Hydrocotylo-Baldellion, Nanocyperion flavescentis, Caricion davallianae and Junco-Molinion, as well as some undefined vegetation types of the order Molinietalia. So, although A. tenella has always been a rare plant at the northeastern fringe of its area, it did not show a striking selectivity as to its habitat or vegetation type. Therefore its rarity in the Netherlands is not very easy to explain, its frost sensitivity accounting only for the rough course of its eastern limit. The decline of the plant in this country is mainly due to drainage and eutrophication. However, ceasing of human activities like cutting sods or mowing has also contributed to its disappearance from many sites in the dunes and in moorland areas. Nearly all present sites are situated in nature reserves, where the plant is protected against drainage and eutrophication influences. Nevertheless, the management of these reserves is of vital importance for the populations of A. tenella, some kind of human interference being required for their survival in most cases.