On the variation in the flower heads of Aster tripolium L. in the Netherlands

In the Netherlands Aster tripolium L. exhibits a considerable variation in the number of ray florets per capitulum. There is a gradual transition from plants producing inflorescences with ray florets to plants producing exclusively flower heads without a single ray floret (so-called discoid plants). Discoid plants are particularly frequent in the south-western parts of the Netherlands, the populations occurring along the western Scheldt estuary (Westerschelde) showing the highest percentages of discoid specimens, but in the northern part of the country they are far less common. Discoid forms are chiefly found outside of the dikes. The number of ray florets per capitulum is not correlated with the number of disk florets. Accordingly, the recognition in the area of the Low Countries of varieties based on the number of ray florets does not seem to be recommendable.