Seeds of Thalictrum mirabile (Ranunculaceae) require cold stratification for loss of nondeep simple morphophysiological dormancy

Seeds of the eastern North American herbaceous polycarpic perennial Thalictrum mirabile small have differentiated but underdeveloped (small) embryos that are physiologically dormant at maturity in September. Physiological dormancy was broken effectively by cold stratification at 1°C, but embryos required temperatures ≥15:6°C for growth after physiological dormancy was broken. Gibberellic acid substituted for cold stratification. Breaking of physiological dormancy in seeds exposed to natural temperatures in a greenhouse occurred during winter, and embryo growth and germination occurred in late winter - early spring. Furthermore, seeds in the greenhouse remained viable until the second and third (spring) germination seasons. Thus, T. mirabile seeds have the capacity to form a short-lived persistent soil seed bank. Buried seeds of T. mirabile apparently go through an annual dormancy-nondormancy cycle. Seeds buried in September 1994 were nondormant when exhumed in April 1995 and April 1996 and incubated in light at 25:15°C for 2 weeks, but they were dormant in June 1995 and September 1995. Seeds of T. mirabile have nondeep simple morphophysiogical dormancy. This is the first report of nondeep simple morphophysiological dormancy being broken by cold, and not by warm, stratification.