Seed germination traits in the rare sandstone rockhouse endemic Solidago albopilosa (Asteraceae)

Understanding how temperature and other environmental cues influence germination traits can aid in the conservation and management of rare plant species. We examined the germination niche of the narrow endemic Solidago albopilosa, a perennial herb restricted to sandstone rockhouses in the southeastern United States. We experimentally subjected seeds to varying lengths of cold stratification, incubation temperatures, photoperiods, and seasonal temperature cycles that simulated current ambient temperatures and a climate warming scenario. Seeds exhibited conditional physiological dormancy and germinated at greater proportions following chilling than when fresh in all temperatures and light regimes tested. In seasonal temperature cycles that simulate those after seed dispersal in late autumn, seeds began germinating after 9 wk in late-winter temperatures (February), with peak germination occurring in early spring (March). Germination timing shifted 1 wk earlier in the spring with climate warming, but germination proportions did not differ among treatments. Buried seeds did not persist to the second germination season (spring), suggesting minimal carryover among years. Seed viability declined in the smallest (< 50 stems) populations but varied less among sites with different levels of human disturbance. A germination niche defined by conditional physiological dormancy, a minimal chilling requirement, dark germination, seasonal germination cueing, and low persistence in the soil is consistent with the expectation of a perennial herb from a stable habitat, but diverges in some aspects from seed traits found in Solidago species of grasslands and open habitats. These results suggest that dormancy or germination do not limit seed regeneration in most natural populations nor contribute to S. albopilosa's rarity.