Seed dormancy and germination of three Corydalis species, disjunct relict species in East Asia.

Disjunct congeneric species are common in the temperate flora of Europe, East Asia and eastern North America. However, it is unclear whether the kind of seed dormancy is maintained after divergence. This study aimed to determine the type of seed dormancy of three Corydalis species native to Korea and examine whether the dormancy trait has been conserved after long-term separation. We examined embryo growth and germination characteristics of C. remota, C. incisa and C. speciosa through phenology experiments, controlled temperature experiments, stratification treatments and GA3 application. All three species had underdeveloped embryos at dispersal and exhibited morphophysiological dormancy (MPD). C. remota and C. incisa required exposure to warm followed by cold temperatures for embryo growth and germination, and gibberellic acid (GA3) treatment failed to promote germination, indicating that both species have deep simple regular MPD. By contrast, C. speciosa embryos grew and germinated under cold conditions, and while germination was further enhanced by prior warm exposure, GA3 did not overcome dormancy, suggesting that C. speciosa has non-deep complex regular MPD. In all three species, embryo growth occurred in late autumn to winter with germination and seedling emergence in late winter to early spring. Whereas all three species had the same class of dormancy (MPD), differences in temperature responses were found among them. This pattern, consistent with findings from congeneric members on other continents, indicates that MPD is conserved within the genus, whereas specific dormancy levels have diversified in response to regional environmental conditions.