Seed germination ecology of Lesquerella lyrata Rollins (Brassicaceae), a federally threatened winter annual

Lesquerella lyrata Rollins (Brassicaceae) is a federally threatened winter annual that is endemic to northern Alabama (USA). Seeds are dormant at maturity in May and have a high temperature (e.g., 25/15 degrees C, 30/15 degrees C) requirement to break dormancy; low temperatures (e.g., 5/5 degrees C, 15/6 degrees C) cause nondormant seeds to reenter dormancy. Seeds buried in soil and exposed to natural seasonal temperature changes in a nonheated greenhouse came out of dormancy in summer and reentered it in winter, thus exhibiting an annual dormancy/nondormancy cycle. The highest germination percentages of non-dormant seeds in the laboratory were obtained at 30/15 degrees C, in light. Fresh seeds sown on the soil surface in the greenhouse in June germinated in September, when maximum and minimum daily temperatures were about 27 degrees C and 18 degrees C, respectively. Seeds germinated in six autumns in soil samples kept in the nonheated greenhouse for 10 years; thus the species has a long-lived seed bank. Plowing, mowing, and/or grazing to maintain the field, roadside, and/or pasture habitats of L. lyrata in an early stage of succession should be done from June to August, while the species is in the seed stage of its life cycle. These efforts are not needed to promote seed germination per se but to keep the habitat open and, thus, to promote plant growth and seed production. The presence of a seed bank means L. lyrata can persist at a site without producing seeds every year.