De verspreiding van Nymphaea candida Presl en Nymphaea alba L. in Nederland

An investigation has been made on the distribution of Nymphaea alba and N. Candida in the Netherlands. During 1977 7 new localities of N. Candida were discovered, while from three other localities material was present in the Rijksherbarium Leiden, so that now 11 localities of the species are known. The distribution in the Netherlands seems to be discontinuous and is restricted to a part of the Fluviatile district and the borders of the Drenthian district, in the northern part of the country (fig. 1). The discovery of the species by TÜXEN (1955) in Niedersachsen may indicate, that the species can be expected to occur in more localities in northwestern Germany, connecting the northern localities in the Netherlands with those of the main area in eastern Europe. N. alba has been found during our investigations in 48 localities, while the material present in the Rijksherbarium has also been checked ( fig. 2). The numbers of flowers present in the Rijksherbarium and the data they were collected are shown in fig. 3. All records of waterlilies (recorded as N. alba) are summarized in fig. 4, which shows that they seem to be absent in the brackish water areas of Zeeland, the Haarlemmermeerpolder, Noord-Holland, the northwestern part of Friesland and the north of Groningen (average chlorinity above 300 mg/l.).