Morphophysiological dormancy in seeds of two North American and one Eurasian species of Sambucus (Caprifoliaceae) with underdeveloped spatulate embryos

In contrast to previous reports, the endocarps ("seed coats") of Sambucus s pecies are nor impermeable to water; thus, the seeds do not have physical d ormancy. Seeds of the North American species Sambucus canadensis and S. pub ens and of the European species S, racemosa have spatulate shaped embryos t hat are similar to 60% fully developed (elongated) at seed maturity. The em bryo has to extend to the full length of the seed to germinate. Embryos in freshly matured seeds of S. canadensis and in those of S. pubens ns grew be tter at 25 degrees /15 degreesC than at 5 degreesC, whereas the rate of emb ryo growth in S. racemosa was higher at 5 degreesC than at 25 degrees /15 d egreesC. Seeds of all three species germinated to significantly higher perc entages in light (14-h photoperiod) than in darkness. Fresh seeds of neithe r species germinated during 2 wk of incubation over a range of thermoperiod s. Warm followed by cold stratification broke dormancy in seeds of S. canad ensis and in those of S. pubens. Thus, seeds of these two North American sp ecies have deep simple morphophysiological dormancy (MPD). In comparison, s eeds of the European species S. racemosa required a cold stratification per iod only for dormancy break, and thus they have intermediate complex MPD. G A, was much more effective in breaking dormancy in seeds of S. racemosa tha n it was in those of S. canadensis or S. pubens.