De zoetwatergetijde-dotter van de Biesbosch en de Oude Maas: Caltha palustris L. var. araneosa, var. nov

In tidal freshwater swamps c.q. river banks in the Biesbosch and Oude Maas (tidal level difference ca. 2 m), 51°45’ N, 4°30’-4°35’ E, a special ecological race of Caltha palustris L. occurs, here newly described as var. araneosa. Its tall, erect, multiflorous stem is characterized by elbow-like thickened nodes (fig.l), producing an axillary turion-like vegetative sprout (fig. 2, a and d), with roots, emanating from the nodes (fig. 2, a), similar to those of the common form (fig. 2, c). These elbow-like thickened nodes with an axillary turion-like vegetative sprout are absent in the common form (fig. 2, b). After decay of the stem these nodes with roots form a spider-shaped, vegetative diaspore described in an earlier paper (VAN STEENIS, 1968). This seems to be the common method of dispersal under the unusual tidal environmental conditions. Transplantation experiments of the turions have shown that the same characters are maintained under constant water level conditions and from transplanted specimens similar turions were thus obtained. Control experiments simultaneously executed showed that normal Caltha palustris did not show anything similar. It is also shown that besides serving for attachment, the roots of the turions could provide the node with its buoyancy power. Var. araneosa is assumed to have the same taxonomic rank as var. radicans sens. stricto.