Enkele gegevens over de standplaats van Hypericum canadense L

Hypericum canadense L. is an amphi-atlantic species, known in Europe from two localities only: Lough Mask in Ireland and northeastern Twente in the Netherlands. The habitat of the species on the western shore of Lough Mask is described with the help of four sample plots, and this site is compared with the habitat at Farnham, Quebec, Canada. The Irish habitat is a complicated and rare ecosystem. On the basis of a water-logged sandy soil which is superficially inundated during a major part of the year and moreover poor in lime, mesotrophic and extensively grazed, it presents four gradients: (1) a ‘macro-gradient’ from the calcareous soils east of Lough Mask to the silurian slates at its western shore; (2) a ‘meso-gradient’ starting from alternating low sandy ridges, from which sand is blown over marshy depressions; (3) a ‘minigradient’ from depressions poor in humus or running dry for a short time to depressions rich in humus or running dry for a longer time; (4) a ‘micro-gradient’, being a grazing pattern of tussocks and hollows. The conclusion is drawn that Hypericum canadense appears to be a long-established native species and not a neophyte. In this respect the author agrees with WEBB (1957, 1958) and JONKER (1935, 1959). However, no argument is found in favour of the supposition that a relic species is concerned. The specialized gradient ecosystem which Hypericum canadense appears to require in Europe may in itself be a sufficient explanation for its rareness and discontinuous distribution.