Arenaria fontinalis (Short & Peter) Shinners (Caryophyllaceae) is endemic to wet limestone cliffs and ledges in north-central Kentucky and north-central Tennessee. Seeds are dispersed from mid-May to early July and germinate in September and October. Plants overwinter as semi-rosettes and flower and set seeds the following spring; thus, they behave as winter annuals. Seeds are dormant at maturity in spring, afterripen during summer and are nondormant by autumn. Seeds afterripened when alternately wetted and dried in an unheated greenhouse and in an incubator at 30/15°C and when kept continuously wet in incubators at 15/6, 20/10 and 30/15°C. Seeds did not afterripen when stored dry at ambient laboratory conditions. The peak of germination for seeds sown on soil in the unheated greenhouse in the springs of 1981, 1982 and 1983 occurred the following autumn, when mean daily maximum and minimum temperatures were about 25 and 15°C, respectively. Germination of 1-3% of the seeds was delayed until the second autumn after sowing. Plants are day-neutral, and some of them will flower without vernalization. Plants kept in the unheated greenhouse during winter were much healthier and survived better than those kept in a heated greenhouse.