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Perennial herb from a long, vertical and horizontal, rhizome-like, deep-seated root; stems erect, solitary, few-branched above, glabrous below, usually glandular-bristly above, hollow, exuding milky juice when broken, 0.4-2.0 m tall.
Basal leaves lacking; stem leaves alternate, prickly-margined, deeply lobed or pinnately cut, 6-40 cm long, 2-15 cm wide, with clasping leaf bases, upper leaves reduced.
Heads with strap-shaped flowers, several on glandular stalks in an open, flat- or round-topped inflorescence, relatively large, commonly 3-5 cm wide in flower; involucres 14-22 mm tall; involucral bracts lanceolate, tapering to a slender tip at the apex, glabrous, obscurely woolly-hairy or more or less copiously covered with coarse, spreading, gland-tipped hairs and often with tufts of woolly-hair as well, outer ones often becoming ridged-thickened in age; ray flowers yellow.
Achenes 2.5-3.5 mm long, ribbed, cross-wrinkled; pappus of white hairlike bristles.
Two varieties occur in BC:
1. Involucres and stalks of the heads with coarse, spreading, gland-tipped hairs................. var. arvensis
1. Involucres and stalks of the heads glabrous or obscurely woolly-hairy...................... var. glabrescens Guenth., Grab. & Wimm.
Source: The Illustrated Flora of British Columbia