DEEP COMPLEX MORPHOPHYSIOLOGICAL DORMANCY IN SEEDS OF THE MESIC WOODLAND HERB DELPHINIUM TRICORNE (RANUNCULACEAE)

Delphinium tricorne Nutt. is an herbaceous perennial of mesic deciduou s forests in eastern North America. Seeds have underdeveloped linear e mbryos that must grow from about 0.5 to 2.4 mm before seeds can germin ate, and this growth occurs only at low temperatures. At 5 degrees C a nd in a nonheated greenhouse during winter, the peak of embryo growth occurred after seeds had received 10-12 wk of stratification, indicati ng that the embryos were physiologically dormant. Thus, seeds have mor phophysiological dormancy (MPD). Although seeds are dispersed in late spring and are exposed to high temperatures during summer, stratificat ion is the only requirement for dormancy loss, embryo growth, and germ ination; GA(3) did not substitute for stratification. Therefore, seeds have deep complex MPD. In nature, seeds are stratified during late au tumn and winter and germinate at low temperatures in late February and early March, about 2 mo before canopy closure. The optimum germinatio n temperature in laboratory studies was 5 degrees 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.