Interpopulation and Interyear Variation in Germination in Scotch Thistle, Onopordum acanthium L., Grown in a Common Garden: Genetics vs Environment

Germination patterns were studied among three populations of Scotch thistle, Onopordum acanthium L. (Asteraceae). Cypselas (seeds) were collected twice during the growing season for four consecutive years (1996-1999) from plants grown in the same location, the Environmental Sciences Western Field Station (ESW) near London, Ontario. Cypselas from 1996 came from plants that had been transplanted as rosettes from their original sites to ESW, while those for 1997-1999 came from plants grown from cypselas collected in 1996. Fresh cypselas were put to germinate at 25 °C, 14 h light/10 °C, 10 h dark for 55 days. Consistent and significant differences in final germination percentages among populations were obtained over the four years. There were also differences between collections within populations in 1996 and 1998. In addition, the final germination percentage (collectively) differed widely among years. There was a greater than 30 percent correlation between germination percentage and mean daily maximum temperature during cypsela maturation. Since there were similar differences among populations every year, it appears that germination patterns of O. acanthium populations have a genetic basis as well as an environmental one.