Het verspreidingsgebied van Senecio jacobaea L. var. nudus Weston

In Senecio jacobaea L. two forms with non-radiating capitules are distinguished: a.) a non-heritable form, hence of no systematic value, occurring incidentally throughout the area of the species, with the outer ray of fruits nearly glabrous like in normal radiating forms of the species, and b.) a heritable (DE VRIES, 1901) form with a distinct area (fig. 1) with all fruits equally hairy (probably by reduction of the outer ray of flowers). The distribution of the latter form, provisionally called Senecio jacobaea var. nudus Weston (Bot. Univ. 3, 1772, p. 641; syn.: S. jacobaea var. floseulosus Lamk. et DC.; S. dunensis Dum.), is given from herbarium material and literature; var. nudus fully replaces the type variety in the dunes in the Netherlands southwards to IJmuiden, only in the dunes between IJmuiden and Den Haag both the radiating form and var. nudus are found together (at present the latter is very common whereas the radiating form is rare, but at the end of the last century this situation was reverse). Var. nudus may be worth the rank of subspecies. A probable hybrid S. aquaticus X jacobaea var. nudus is recorded from the island of Terschelling.