Field Guide to Noxious and Other Selected Weeds of British Columbia
Bull Thistle (Cirsium vulgare)
taprooted biennial with spiny winged stems growing 0.3 to 1.5 metres tall; leaves end in long, sharp spines; upper surface with short prickles, undersurface cottony; flowerhead bracts tipped with prickles; purple flowers 4 to 7.5 cm across
often confused with Canada thistle (Cirsium arvense) which has creeping roots, much smaller flowers and weak prickles, not spines on the leaves
