In Japan, the herbaceous perennial Corydalis ambigua Cham. et Schlecht. occurs in Tohoku and Hokkaido, where it grows in deciduous woodlands. Seeds have an underdeveloped embryo that is physiologically dormant at the time of dispersal in late May. In laboratory experiments, embryos did not grow when kept continuously at 5 °C or at alternating diurnal temperatures of 25/15 °C. However, following warm stratification at 25/15 °C, they grew at 15/5 °C and continued to do so at 0 °C. Radicles emerged after a relatively long period at 0 or 5 °C, following warm stratification at 25/15 °C and then incubation at 15/5 °C. Embryos began to develop in autumn in seeds under near-natural conditions in a metal frame-house, and they had grown to an average of about 90% of their full length by December. Beginning in December, the seed coat split, exposing the endosperm, and in March both the radicle and the cotyledon emerged under the snow or immediately after snow melt. Dormancy in seeds of C. ambigua is the same as that in seeds of Hydrastis canadensis L., which has been described as a special type of deep simple epicotyl morphophysiological dormancy.Key words: Corydalis ambigua, embryo growth, morphophysiological dormancy, seed germination phenology, underdeveloped embryo.
