Deep Complex Morphophysiological Dormancy in Seeds of the Mesic Woodland Herb Delphinium tricorne (Ranunculaceae)

Delphinium tricorne Nutt. is an herbaceous perennial of mesic deciduous forests in eastern North America. Seeds have underdeveloped linear embryos that must grow from about 0.5 to 2.4 mm before seeds can germinate, and this growth occurs only at low temperatures. At 5⚬C and in a nonheated greenhouse during winter, the peak of embryo growth occurred after seeds had received 10-12 wk of stratification, indicating that the embryos were physiologically dormant. Thus, seeds have morphophysiological dormancy (MPD). Although seeds are dispersed in late spring and are exposed to high temperatures during summer, stratification is the only requirement for dormancy loss, embryo growth, and germination; GA3 did not substitute for stratification. Therefore, seeds have deep complex MPD. In nature, seeds are stratified during late autumn and winter and germinate at low temperatures in late February and early March, about 2 mo before canopy closure. The optimum germination temperature in laboratory studies was 5⚬C. This is the first report of deep complex MPD in the Ranunculaceae, and it increases to five the number of types of MPD known to occur in the family.