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RESEARCH PRODUCT

The comparative biology of the closely related Senecio nebrodensis and S. viscosus, a narrow endemic and a widespread ruderal

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The closely related Senecio nebrodensis, a perennial herb from four mountain ranges in Spain, and S. viscosus, an annual herb widespread in Europe, are being compared by the study of herbarium material and comparative cultivation. In cultivation, S. nebrodensis behaved as an annual, completing its life cycle within a shorter period of time than S. viscosus. The formation of basal leaf rosettes is much more pronounced in S. nebrodensis than in S.viscosus. The main difference between the two species, however, is their breeding system. While S. nebrodensis is self-incompatible, S. viscosus is self-compatible. Differences in reproductive morphology (mainly size and number of ray florets) are suggested to be related to this difference in breeding system. Despite differences in disc floret number and capitulum number observed in the cultivated material, the potential reproductive output of the two species is roughly comparable. Senecio viscosus is believed to be a descendant of S. nebrodensis. It is postulated that the former differentiated from thelatter at the latest in glacial or early postglacial times. Following postglacial climatic changes, S. nebrodensis retreated into high altitudes, while S. viscosus, adapting to these changes, expanded northwards. The strikingly different degree to which the two species exploit man-made disturbances is interpreted as being due to a difference in opportunity: In its climatically defined range S. nebrodensis experiences little disturbance. Senecio viscosus, on the other hand, inhabits areas strongly disturbed by human activity. It is concluded that S. viscosus shows no obvious adaptations to its habitat, but is well preadapted.