THE BIOLOGY OF CANADIAN WEEDS.: 84. Oenothera biennis L.

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Abstract
Oenothera biennis L., the common evening-primrose, is a widespread weed of roadside and waste places commonly occuring on light sandy or gravelly soils where competition is limited. The species is native to North America and, although occurring in all 10 Canadian provinces, is more common in the east than in the west. The chief factor contributing to its success as a weed is the ability to tolerate drought. A winter annual or facultative biennial, it flowers and bears seed only once in a lifetime. The small, irregularly shaped seeds have a high oil content, and contain γ linolenic acid, an uncommon fatty acid of pharmaceutical value. Oenothera biennis is a true-breeding translocation heterozygote composed of two genomes (complexes) differing genetically as well as in chromosomal end arrangement. Populations of O. biennis consist of numerous inbreeding lines, between which limited hybridization may occur.Key words: Common evening-primrose, Oenothera biennis, weed biology, population structure