Seed dormancy vs. climate at site of origin
Factor loadings of climatic variables on PCs are shown in Table 3 and Figure S4 . Within Fennoscandia, mean temperature of the warmest month and of the warmest quarter decreased with PC1, while mean annual precipitation and mean precipitation during the warmest quarter increased with PC1. Annual temperature was instead negatively associated with PC2. For seeds produced by Fennoscandian populations in the greenhouse, germination proportions quantified 1 and 3 weeks after seed maturation tended to increase with PC1 (germination proportion 1 week: partial linear regression coefficient, β = 0.0387, P = 0.033; germination proportion 3 weeks: β = 0.0799, P = 0.003, Table 4 ), whereas no association was found with PC2 or PC3. Seed dormancy thus tended to be stronger in populations from sites with relatively high summer temperature and low precipitation than in populations originating from sites with low summer temperature and high precipitation.
Within Italy, temperature variables increased with PC1, and precipitation variables increased with PC2 (Table 3 ). Mean annual precipitation was positively associated with PC3, while mean precipitation during the warmest quarter showed an opposite trend (Table 3 ). Germination proportions of seeds produced by Italian populations in the greenhouse were very low 1 and 3 weeks after seed maturation (Fig. 3A ) and were not significantly associated with any PC.
No significant association was found between PCs and germination proportions of seeds 12 weeks after harvest in the greenhouse or in the field (Table 4 ), and mean germination proportions did not vary with latitude or longitude of origin in either region (P>0.05, not shown).