GERMINATION ECOPHYSIOLOGY OF ARENARIA GLABRA, A WINTER ANNUAL OF SANDSTONE AND GRANITE OUTCROPS OF SOUTHEASTERN UNITED STATES

The germination ecophysiology of Arenaria glabra Michx., a characteristic winter annual plant species of granite and sandstone outcrops of southeastern United States, was investigated. Seeds germinate in early autumn, plants overwinter in the rosette stage and then flower, set seeds, and die in late spring; seeds are dispersed soon after maturity. Eighty‐five to 90% of freshly‐matured seeds were innately dormant, and the other 10–15% germinated only at temperatures lower than those that occur in the habitat at the time of seed dispersal in June. During the summer after‐ripening period, seeds stored dry under ambient laboratory conditions exhibited progressive increases in rates and total percentages of germination, a widening of the temperature range for germination, and a loss of the light requirement. At a 14‐hr daily photoperiod, seeds kept on continuously moist soil germinated to 83% at simulated July and August temperatures during July and August, and the remainder germinated at September temperatures in September. On the other hand, seeds subjected to alternate wetting and drying during July and August germinated to only 9% during those 2 months, and the remainder germinated after the soil was kept continuously moist, beginning on 1 September, at simulated habitat temperatures during September and October. Thus, the timing of germination of A. glabra in the field is controlled by an interplay of the seeds' physiological state with the dynamics of temperature and soil moisture conditions.