Epicotyl dormancy in the mesic woodland herb Hexastylis heterophylla (Aristolochiaceae)

Seeds of the woodland herb Hexastylis heterophylla (Ashe) Small (Aristolochiaceae) were incubated in two sequences of temperature regimes: (a) warm → cool → cold → cool → warm, and (b) cold → cool → warm → cool → cold → cool → warm. In the first sequence, roots emerged during the first cool period ("autumn") and shoots during the second cool period ("spring"). In the second sequence, roots emerged during the second cool period ("autumn") and shoots during the third cool period ("spring"). Thus, in seeds of H. heterophylla, a period of warm temperatures is required for subsequent emergence of roots at cool ("autumn") temperatures and a period of cold ("winter") temperatures is required for subsequent emergence of epicotyls (shoots) at cool ("spring") temperatures (in seeds with roots emerged). These dormancy-breaking and germination requirements demonstrate clearly that seeds of this species have deep simple epicotyl morphophysiological dormancy (epicotyl dormancy), like those of Asarum canadense L., another eastern North American woodland herb in this family. This is the first report in the literature on seed dormancy in Hexastylis and only the third one for Aristolochiaceae.