Standplaats, stengelhoogte en levensduur van Inula conyza DC. in Nederland

On the Schiepersberg (Cadier en Keer, province Limburg) Inula conyza can not be classified as biennial in the definition of the ‘Flora van Nederland’. It has been observed during the summers of 1975—1977 that on the one hand the leaf rosette stage persisted for at least three years and on the other hand a considerable number of individuals reached the flowering and setting stage only after two years of rosette stage. A small minority of the individuals showed their vigour by both flowering in two successive summers and developing more than one stem in both years. According to these observations the Dutch flora’s definition of a biennial has been reconstructed in the following way: a plant which (in its natural habitat) usually flowers and sets only once and at the earliest in its second calendar year. In this sense I. conyza behaves in the Netherlands as a biennial, however the hypothesis has been put forward that I. conyza may behave as perennial in submeridional Europe, which is its distribution centre. Beside the localities with I. conyza on the Schiepersberg, we have studied a number of other Dutch localities of this species. All the sites of both the Chalk and the Fluviatile phytogeographical districts were shown to be of anthropogenic origin (such as fallow fields and pastures, limestone quarried, dikes), only in the calcareous Dune district were natural habitats found. A general characterisation of the site of I. conyza in the Netherlands could be as follows: extremely well drained, exposition in the southern quadrant, full to intermittent sunlight exposure, without both contemporary grazing and sand-shifting, calcareous substratum and an open vegetation cover in the lowest herb layer. I. conyza is exceptionally abundant on fallow fields and abandoned pastures. The stem height of I. conyza correlates negatively with the openess of the habitat