A latitudinal cline in vernalization requirement in Cirsium vulgare

We studied geographical variation in the vernalization requirement among European populations of the facultative biennial thistle Cirsium vulgare In two common garden experiments and a growth room experiment we found genotypes that flowered without cold, in their first year These annual types originated mainly from the south of Europe Most of the plants from the northern populations flowered in their second year, after experiencing winter cold We discuss the effects of the absence of a vernalization requirement on the phenotype