Common groundsel adapts readily to new environments and selection pressures and has been variably described as both a winter and summer annual. We characterized germination response to temperature in seeds from populations occurring at six sites along a 700-km north–south transect (Kentucky to Michigan). Seeds were collected in 2000 and 2002 from randomly selected plants (350 to 400), at each sampling site. Two germination patterns were observed: (1) seeds from the southern locations averaged 80 to 90% germination across the range of 5 to 25 C; and (2) seeds from northern locations had reduced germination when incubation temperatures were close to 5 or 25 C. When seed from all locations were grown in a common environment (14/10-h thermoperiod of 22/18 C), their progeny had a germination response that was similar across the temperature gradient, regardless of original location, suggesting germination of the parent seed was due to maternal environmental effects. In a subsequent experiment, common groundsel was grown in growth chambers with warm long days (22/15 C and 16 h of light), warm short days (8 h of light), cold long days (15/8 C and 16 h of light), and cold short days. Eighty percent of seeds from the warm environments germinated across the range from 5 to 25 C indicating that these maternal conditions had produced nondormant seeds. In contrast, 20% or fewer of the seeds from plants in the cold chambers germinated regardless of temperature, suggesting that dormancy had been induced by the cool maternal environment. Results also indicated that signaling of maternal environment varied with inflorescence development stages, meaning the earlier the inflorescences are exposed to cold conditions, the lower the percent germination in F1 seeds. Preventing seed maturation on common groundsel growing under cool conditions may reduce the formation of a persistent seed bank.
Nomenclature: Common groundsel, Senecio vulgaris L. SENVU