Salt contamination of soils has been studied in a range of habitat types of groundsel (Senecio vulgaris L.). Evidence suggests that roadsides salted in winter and areas around salt dumps have high mean values of exchangeable sodium; lower values have been found for coastal areas, and inland sites not known to be salted.

Salt tolerance tests-both in Petri-dish experiments and in soils irrigated with different salt solutions-suggest that topodemes from sites subject to salting are, in general, more salt tolerant than those from non-salted areas. This apparently simple relationship is critically examined. Genecological implications of salt tolerance patterns are fully discussed.