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Foeniculum vulgare Mill. (Apiaceae) is a perennial hemicryptophyte native of the Mediterranean basin. In Israel, natural populations are distributed across different habitats and phytogeographical territories. To evaluate the occurrence of intra-specific adaptive traits, we studied the germination of mericarps, collected along a rainfall/altitude gradient, in response to constant and alternating temperatures. Germination response to the different temperature regimes was population specific (p<0.001), either when expressed as final percentage of germination (%G) or as germination rate (G50 and probability density functions). Southern-distributed populations exhibited higher %G as compared to northern ones under all temperature regimes. This in spite of the overall 50% decrease in %G at warmer constant and alternating temperatures that characterized the first.

Temperature fluctuations prolonged the germination period of all populations by two to seven days, as compared to constant temperatures (7-13 days period), and populations responded differently to different fluctuation's factors, e.g. temperature amplitude, minimum and/or maximum temperature.

Significant associations between germination (%G) and environmental variables was found e.g., January temp. (r = 0.62 to 0.70), rainfall (r = -0.58 to -0.84) and altitude (r = ca. -0.7).

Weight of mericarp varied significantly (p<0.01) among populations, with heavier fruits developing at rainier sites (r = 0.7); this had no influence on germination. Variability in the germination response to temperature of mericarps from different habitats suggests the presence of population-specific adaptive traits in response to environmental pressure. Whether these are exclusively the result of parental effect or of the interaction between edaphic conditions and genetic-determined germination characters, remains to be determined.