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Perennial, aromatic, evergreen shrub; stems solitary or branched from the base with shredding, grey or light brown bark when older, or with a dense, grooved, white-woolly hairiness when young, 0.1-2.0 m tall.
Principal leaves unstalked or short-stalked, silvery-hairy, typically wedge-shaped with 3 blunt teeth at the tips or sometimes 4-9 toothed or shallowly lobed, 1-4 (rarely 6) cm long, 2-13 mm wide.
Heads discoid, numerous in a narrow to broad inflorescence; involucres narrowly bell-shaped, 3.0-3.8 mm tall; involucral bracts elliptic to obtuse, greyish-hairy; receptacles glabrous; female flowers absent; disk flowers 3-6, sometimes up to 12 at higher elevations.
Achenes resinous-granular, rarely short-hairy.
Recently, the var. wyominensis Beetle & A. Young has been reported in BC. At the present time, however, our material has not been studied with respect to this variety thus only our two traditional varieties are recognized here. They may be distinguished as follows:
1. Involucres narrowly bell-shaped, about 4 mm tall and 2 mm wide; plants of arid sites in the steppe and lower montane zones ..... var. tridentata
1. Involucres broader, about 5 mm tall and 4 mm wide; plants of cooler, mesic open sites in the upper montane and subalpine zones ..... var. vaseyana (Rydb.) Boivin
Source: The Illustrated Flora of British Columbia