Canada Thistle

Cirsium arvense is a species of Cirsium, native throughout Europe and northern Asia, and widely introduced elsewhere. The standard English name in its native area is Creeping Thistle. It is a tall herbaceous perennial plant, forming extensive clonal colonies from an underground root system that sends up numerous erect stems each spring, reaching 1–1.2 m tall (occasionally more); the stems often lie partly flat by summer but can stay erect if supported by other vegetation. The leaves are very spiny, lobed, up to 15–20 cm long and 2–3 cm broad (smaller on the upper part of the flower stem). The inflorescence is 10–22 mm diameter, pink-purple, with all the florets of similar form (no division into disc and ray florets). The flowers are usually dioecious, but not invariably so, with some plants bearing hermaphrodite flowers. The seeds are 4–5 mm long, with a feathery pappus which assists in wind dispersal.

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