Over herkenning, voorkomen en oecologie van Weegbreefonteinkruid (Potamogeton coloratus Hornem.) in Nederland

Potamogeton coloratus has probably always been a rare species in the Netherlands and it was assumed to be extinct in this country untill recently.¹ Since 1978, when it was rediscovered on the West Frisian Isle of Texel, it has been recorded at several places in the Dutch sand dunes, on the isles of Texel, Voorne and Schouwen. A remarkable increase has been observed, probably as a result of turf stripping operations in wet dune slacks. Fen pondweed has appeared as a colonist in the clear, shallow and unpolluted water of the newly formed dune-pools, together with a number of other rather rare plant species, often in combination with large amounts of stoneworts. Relevés of such sites are rendered in Table 2. Table 3 shows seven relevés of older slacks, outside the turf-stripping areas. In these, marsh species are prevailing, whereas the true hydrophytes and stoneworts are represented less prominently. Although Potamogeton coloratus and P. polygonifolius usually grow in rather different habitats (the first one usually in calcareous water, the second usually in midly acid water), both were observed together in four of the Texel localities, a combination which was known thusfar only from the Hebrides (Tiree, Benbecula18 and Skye41) and the Irish west coast (Connemara).42 The Isle of Texel seems to be the only place outside the British Isles where this phenomenon can be seen.