Dotterbloem en Waterviolier in Nederland

Data from this century on the distribution of Caltha palustris and Hottonia palustris are used tot illustrate the role of volunteers in a monitoring scheme. Actual patterns in the distribution of the two species are discussed. About 40 percent of these data has been sampled by volunteers. It is demonstrated that both Caltha and Hottonia showed a decline in the period 1975—1989. In contrast to Caltha, the occurrence of Hottonia is strongly linked to areas with seapage water.