Bull Thistle

Bull Thistle

Scientific name: Cirsium vulgare

Common names: Bull thistle

Description: Bull thistle is a common weed in disturbed areas that was introduced to North America in contaminated crop seed. It is a biennial plant. In its first year it grows a rosette of green, somewhat hairy, prickly leaves and in the second year it sends up flower stems that contain large (1.5-2 in. wide) purple flowers. It is commonly found in roadsides, pastures, logged areas, burned areas, and vacant lots. Bull thistle can be confused with other native and non-native thistles of the region.

Impact: Each bull thistle plant can produce up to 4,000 seeds, that can be dispersed long distances by wind. It has the capability of dominating overgrazed pastures, thereby reducing the productivity of grazing land. It can also suppress the growth of tree seedlings through its ability to rapidly spread in forest clear cuts.

Source: KingCounty.gov

For more information, please visit the Noxious Weed resources at KingCounty.gov: http://www.kingcounty.gov/services/environment/animals-and-plants/noxious-weeds/weed-identification/bull-thistle.aspx