Extension > Garden > Diagnose a problem > Is this plant a weed? > Broadleaf Weeds > Basal > Canada Thistle
Cirsium arvense (L.) Scop.
- Prairie and landscape plantings, and lawns
- Perennial that grows to 4’ tall
- Upright stems are grooved, slightly hairy when young, increasingly hairy as they mature, and branched at the top
- Leaves have crinkled edges, spiny margins, and are somewhat lobed
- Flower heads are numerous, compact, and 3/4” or less in diameter; flowers June through Sept.
- Flowers are reddish-purple to purple and are surrounded by bracts without spiny tips
- Root system has underground stems (rhizomes)
- Minnesota Primary Noxious Weed that spreads rapidly and aggressively from the extensive root and rhizome system and by seed