Seed Germination Ecophysiology of the Woodland Herb Asarum canadense

Abstract

Asarum canadense L. is an herbaceous perennial of rich deciduous forests of eastern North America. In N-central Kentucky, flowering begins in midto late April, and seeds are mature by mid-June. Seeds exhibit a type of morphophysiological dormancy known as epicotyl dormancy. Radicle dormancy is broken by high summer temperatures, and shoot dormancy is broken by low winter temperatures. Thus, radicles emerge from seeds during autumn, and cotyledons emerge the following spring. In a nonheated greenhouse, 66% of the radicles emerged in October, when mean daily maximum and minimum temperatures were 22.0 and 10.8 C, respectively, and 84% of the cotyledons emerged in March, when these temperatures were 21.6 and 7.9 C, respectively. Radicle dormancy was broken in seeds incubated at (12/ 12 hr) daily thermoperiods of 20/10 and 30/15 C. Radicles emerged from seeds incubated at 20/10 C, but they did not emerge from seeds incubated at 30/15 C until seeds were transferred to 20/10 C. Radicles emerged from seeds incubated at 30/15 C until seeds were transferred to 20/10 C. When seeds with emergent radicles were cold-stratified at 5 C for 0, 1, 2, 3, 4, 6 and 8 weeks and then moved to spring (20/10 C) temperatures, 0, 0, 0, 1, 9, 47 and 76%, respectively, of the cotyledons emerged. In seeds with epicotyl dormancy, the root system is well-developed when the cotyledons emerge, and cotyledons expand in spring, at the beginning of the most favorable season for photosynthesis in the forest. This temporal separation of radicle and cotyledon emergence may be of adaptive significance in deciduous woodland herbs.