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Annual herb from a short taproot; stems erect, solitary, few-branched above, glabrous, hollow, exuding milky juice when broken, 0.1-1 m tall.
Basal leaves lacking; stem leaves alternate, prickly- margined, lowermost with stalks but not so clearly divided (as in S. oleraceus) into blade and stalk, more or less egg-shaped, uppermost deeply pinnately cut to egg-shaped and lobeless with rounded, clasping flanges at the base, 6-30 cm long, 1-15 cm wide.
Heads with strap-shaped flowers, several on sometimes glandular stalks in an open, flat-topped inflorescence, relatively small, commonly 1.5-2.5 cm wide in flower; involucres 9-14 mm tall; involucral bracts lanceolate, tapering to a slender tip at the apex, glabrous except for some spreading, gland-tipped hairs; ray flowers yellow.
Achenes 2.5-3 mm long, with 3 or rarely 4-5 conspicuous longitudinal ribs on each face, not wrinkled; pappus of white hairlike bristles.
Source: The Illustrated Flora of British Columbia