THE BIOLOGY OF CANADIAN WEEDS. 94. Sonchus arvensis L.

Abstract

Perennial sow-thistle (Sonchus arvensis L.) was introduced into North America from Europe and Asia and is distributed widely throughout the Canadian provinces. Two varieties are common; var. arvensis and var. glabrescens differ morphologically in the presence or absence of glandular hairs on peduncles and involucral bracts, respectively. Both varieties are common along roadsides and river and lake shores and in waste areas and cultivated fields throughout their introduced and native ranges. The perennial nature and ability to spread both by spreading roots and by seed make these weeds difficult to control. Details on the morphology, cytology, distribution, reproductive and population biology, and control methods are reviewed.Key words: Distribution, perennial sow-thistle, smooth perennial sow-thistle, weed biology