The success of rare plant conservation programs depends upon understanding the ecological factors that regulate seed dormancy and germination. In this study, we characterize the germination niche with respect to temperature and light of three imperiled perennials that are endemic to rock outcrops in the southeastern United States: Astragalus bibullatus, Claytonia ozarkensis, and Conradina verticillata. Our results show that a majority of seeds for each species are unable to germinate at habitat temperatures prevailing after dispersal in early summer. Seeds of the rockface endemic Claytonia ozarkensis germinated to high rates in darkness at 5°C, suggesting germination is confined to winter and that seeds are unable to persist beyond one germination season (transient seed bank). For Conradina verticillata, 44% of seeds germinated without cold stratification, while the remainder required cold stratification and light to overcome physiological dormancy. Following cold stratification, Conradina verticillata seeds germinated in light at cool (15/5 °C) but not at warm (30/15 °C) temperatures, although overall seed viability was low (26%). Seeds of Astragalus bibullatus germinated to low rates (< 10%) in seasonal temperature sequences, confirming that this species forms a persistent seed bank. Seeds of Astragalus bibullatus lost viability following heat shock for 30 min at 125 °C, but germinated to > 50% following mechanical scarification and incubation at 30/15 °C. Results from this study can be used to maximize germination for ex situ and reintroduction programs, and provide insight into managing wild populations.
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