Ecological life cycle of Trepocarpus aethusae (Nutt.) ex DC. and comparisons with two other winter annual Apiaceae native to Easthern United States

The southeastern United States endemic plant species Trepocarpus aethusae (Apiaceae) behaves as a winter annual, with seeds germinating in autumn and bolting, flowering, and seed production occurring the following growing season. Vernalization was not required for flowering, and plants flowered under both short and long days. Like seeds of two other winter annuals in the Apiaceae, Chaerophyllum tainturieri and Ptilimnium nuttallii, those of T. aethusae have underdeveloped, physiologically dormant embryos, and thus they have morphophysiological dormancy. Physiological dormancy was broken by warm stratification, and after it was broken embryo growth and germination occurred in 68-73% of the seeds in light and in 52-65% of those in darkness at 15/6, 20/10, and 25/15°C. Unlike seeds of C. tainturieri and P. nuttallii, which can re-enter physiological dormancy in autumn and undergo annual dormancy/nondormancy cycles, only 1-12% of T. aethusae seeds re-entered physiological dormancy. However, T. aethusae forms a long-lived persistent soil seed bank; it mostly is attributed to a delay in loss of physiological dormancy and not to dormancy cycling. A comparison of dormancy-breaking and germination requirements does not reveal any reason why C. tainturieri is more weedy than the other two species of Apiaceae. However, seeds of C. tainturieri mature in late May-early June, those of P. nuttallii in mid to late June, and those of T. aethusae in mid to late August and early September. Thus, C. tainturieri can grow in fields and on roadsides and complete its life cycle before these habitats are disturbed by human activities, but the other two species could not complete their life cycle under these conditions.