NONDEEP SIMPLE MORPHOPHYSIOLOGICAL DORMANCY IN SEEDS OF THE MESIC WOODLAND WINTER ANNUAL CORYDALIS-FLAVULA (FUMARIACEAE)

Embryos in seeds of the winter annual Corydalis flavula are differenti ated but underdeveloped (small) and have physiological dormancy (PD) a t maturity in May. Thus, seeds of this species have morphophysiologica l dormancy (MPD). A high percentage of the seeds lost their PD (afterr ipened) when kept at 12/12 hr daily thermoperiods of 30/15 and 35/20 d egrees C for 12 weeks, a low percentage afterripened at 20/10 and 25/1 5 degrees C and none afterripened at 15/6 degrees C or at constant 5 d egrees C. Seeds required 12 weeks at natural summer temperatures or 8 weeks at 35/ 20 degrees C to germinate to 50% or more after 15 days of incubation at 30/15 degrees C. Since high temperatures are the only d ormancy-breaking treatment required for germination, seeds have nondee p simple MPD. Embryos do not grow until after PD is broken, and thus t hey can not grow in the field immediately following seed dispersal. Af ter PD is broken in summer, embryo growth is prevented by high tempera tures. Embryo growth, followed by germination, occurs when temperature s decrease to 25-30 degrees C (day) and 15-20 degrees C (night) in lat e August and early September. In September, seeds germinated to 59-100 % in light and darkness at 15/6, 20/10, 25/15 and 30/15 degrees C, and up to 83% of buried seeds exposed to natural temperatures germinated in autumn. Although the species lacks the potential to form a large pe rsistent seed bank, germination in a few of the seeds sown in a nonhea ted greenhouse in May 1986 was delayed until the autumns of 1987-1990.