Germination Ecophysiology of the Mesic Deciduous Forest Herb Isopyrum biternatum

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Abstract
Seeds of Isopyrum biternatum mature and are dispersed in mid to late May. The embryo in the mature seed is underdeveloped, grows very little during summer, and elongates rapidly in early autumn. Seeds are nondormant at maturity. High temperatures suppress embryo growth and germination during summer. Seeds germinate in late September and early October, soon after the embryos fully elongate. Freshly matured seeds, incubated at a 14-h photoperiod at diurnal thermoperiods of 15/6 and 20/10 C, started to germinate in early July, and by mid-August 80% or more had germinated. In contrast, seeds kept at 30/15.degree. C during summer and then transferred to 25/15 or 20/10.degree. C in autumn did not germinate until autumn. The germination pattern of l. biternatum differs from that of 25 mesic deciduous woodland herbs with underdeveloped embryos. In I. biternatum the nondormant seeds complete germination in autumn, whereas seeds of the 25 species exhibit morphophysiological dormancy and complete germination in spring.