The biology of Canadian weeds. 130. Amaranthus retroflexus L., A. powellii S. Watson and A. hybridus L.

A review of the biological information published after 1980 is provided for three species of the genus Amaranthus: A. retroflexus L., A. powellii S. Watson and A. hybridus L. The three species are noxious weeds introduced to Canada from southern North America. Their geographical distribution has remained almost unchanged since the original paper published in 1980. The plants exhibit a high phenotypic plasticity and genetic variability and they easily adapt to a multitude of agrestal and ruderal habitats. The seeds contribute to a persistent seed bank; they exhibit a variable dormancy and polymorph germination as a result of maternal, genetic and environmental factors. Growth is rapid and plants produce a large number of viable seeds. The three species have developed multiple resistance to triazine and acetolactate-synthase-inhibiting herbicides. They are alternate hosts to many insects, nematodes, viruses, bacteria and fungi that affect cultivated plants.