Common Groundsel (Senecio vulgarisL. var.vulgaris(2n = 40)) is widespread in the northern hemisphere. In Israel, judging from a herbarium survey, records taken from the Israel Plant Information Center (ROTEM), and field studies, it has a restricted and widely disjunct pattern of geographical distribution, and, thus, is another example of the comparatively large group of weeds in Israel which are extremely stenochorous. The remarkable gaps in its distribution, from the Upper Golan to Mt. Carmel and to the Jerusalem area, are considered primarily to be the result of paleoclimatic changes, whereas its occurrence outside these centers of distribution is probably related to long-distance dispersal events. Natural hybridization ofS. vulgariswith its closest ally,S. vernalisWaldst. et Kit. (2n = 20), results in formation of their shortly ligulate and highly sterile hybrid,S. × helwingiiBeger ex Hegi (2n = 30), which is reported for the first time from the Israel area. Hybrid frequencies of 8.7 and 9.8%, respectively, were found in the two mixed populations examined in the Upper Golan. These are higher than previously reported for two localities of hybridization in Central Europe (1.1 and 1.5%), and probably indicate a closer genetic affinity ofS. vulgarisvar.vulgaristoS. vernalisfrom Israel than toS. vernalisfrom Central Europe. It is likely that reports of radiate variants ofS. vulgarisvar.vulgarisfrom the Israel area, none of which could be confirmed, refer toS. × helwingii.
Natural hybridization between diploid Ficaria calthifolia and tetraploid Ficaria verna subsp. verna in central Europe
