THE BIOLOGY OF CANADIAN WEEDS.: 55.: Ambrosia trifida L.

Giant ragweed, Ambrosia trifida L., is a weed of wet low-lying pastures, cultivated fields, orchards, roadside ditches, river banks, and waste places, particularly in southern areas of Manitoba, Ontario, Quebec and the Maritime provinces except Newfoundland. Original research and published information were incorporated into an account on the biology of this weedy, wind-pollinated species. The airborne pollen is known to cause considerable hay fever.