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Biennial or sometimes perennial herb from a taproot; stems erect, ridged, laxly branched, 0.2-1.8 m tall.
Basal leaves pinnately cut, linear, stalked; stem leaves becoming reduced and unstalked above.
Heads discoid, few to several, in a corymb-like arrangement at the ends of ascending branches; involucres 9-13 mm tall, 6-8 mm wide; involucral bracts oblong, grooved, membranous, the middle and outer ones bearing a relatively narrow, darkened comb-like tip; disk flowers purple to pinkish-purple, rarely white, the sterile marginal ones 18-20 mm long, enlarged at the tips with 5 narrow lobes, the central perfect ones 12-16 mm long.
Achenes dark grey to black, 2.5-3.5 mm long; pappus white, 0.5-2 mm long, rarely lacking.
This species is sometimes difficult to separate from the closely related C. paniculata. The latter, however, has much stiffer, divergent branches that are often again branched with narrower heads.
Source: The Illustrated Flora of British Columbia