The ecology of pigweeds (Amaranthus) in Ontario. I. Interspecific and intraspecific variation in seed germination among local collections of A. powellii and A. retroflexus
In southwestern Ontario, Powell's pigweed (Amaranthus powellii S. Wats.) is represented by two morphologically distinct variants. The species is nearly as frequent as redroot pigweed (A. retroflexus L.) in cultivated fields and the two species have often been confused with each other.A germination test was performed with seeds of five local collections of A. retroflexus, two of one variant of A. powellii and four of the second variant of A. powellii. Very little variation in germination behavior was revealed between the collections of A. retroflexus, but great variability occurred between the collections of the latter species. Further germination tests under contrasting light regimes with seeds of two collections of each species affirmed these findings.Seeds of A. retroflexus stored from 5 to 20 weeks before testing yielded more than 75% germination in all tests except in continuous darkness at alternating temperatures (30–18 °C), when 56 to 63% germinated. The total percentage germination of seeds of A. powellii varied between 19% and 95% over the range of test regimes and collections examined. In one collection of A. powellii significantly more seeds germinated in alternating light and darkness than in continuous darkness while the reverse was true in another collection. Seeds from this latter collection developed secondary dormancy when put to germinate in alternating light and darkness.