Seasonal changes in the germination responses of buried seeds of three native eastern North American winter annuals

Long-term studies of seasonal changes in temperature and light : dark requirements for germination were conducted on seeds of Plantago virginica (87 months), Silene antirrhina (32.5 months) and Triodanis perfoliata (36.5 months), buried under natural temperature regimes in central Kentucky, USA. Seeds of P. virginica exhibited an annual conditional dormancy/non-dormancy cycle; thus, the species has the potential to behave as a facultative winter annual. Seeds of T. perfoliata and S. antirrhina had an annual dormancy/non-dormancy cycle, but dormancy induction was not completed until April or May. Thus, depending on the year, 3–21% and 1–97% of the S. antirrhina and T. perfoliata seeds, respectively, germinated in March and these species also have the potential to behave as facultative winter annuals. Data from long-term buried seeds studies in central Kentucky are now available for 16 native (including the three species reported in this paper) and nine non-native winter annuals of eastern North America. Buried seeds of non-natives, as well as those of natives whose geographic range extends beyond eastern North America, tend to have a conditional dormancy/non-dormancy cycle, while those of natives with a range restricted to eastern North America tend to have a dormancy/non-dormancy cycle. However, testing of this hypothesis will have to await data for more winter annuals so that a phylogenetically independent analysis can be conducted.