To improve understanding of the physiology, ecology and regeneration requirements of black poplar (Populus nigra L.), a severely endangered tree species in Europe, we analysed the biochemical composition of seeds from 20 families derived from open pollination of 20 trees in two contrasting environments in France, along the Drôme and Loire rivers. Significant between-family differences were detected. Total lipid contents differed qualitatively between seed of the two populations and were higher in Drôme population (214 ± 29.8 versus 172 ± 19.8 mg.g-1 dw). Soluble sugars were less abundant in seeds of the Drôme population (78.8 ± 10.0 versus 104 ± 25.3 mg.g-1 dw). The protein content (322 ± 74.3 mg.g-1 dw) and quantity of reserve proteins did not differ between seeds of the two populations. Measurements in three consecutive years showed that seeds of the Loire population had significantly higher dry weight (0.69 ± 0.10 versus 0.45 ± 0.10 mg.g-1 dw), but this did not significantly affect the germination rate or root growth of the seedlings measured 5 days after sowing. However, one group of Loire seedlings had substantially longer juvenile roots than another group. Overall, the results suggest that intrinsic qualities of the seeds are not critical factors in early stages and in selection pressure of the species' life cycle and recruitment.