Shrubs, 60-80(-150) cm (plants highly aromatic, crowns flat-topped). Vegetative branches of nearly equal lengths. Leaves (vegetative branches) broadly cuneate, 1.2-3.5 × 0.3-0.7 cm, regularly 3-lobed to irregularly toothed. Heads in paniculiform arrays 10-15 × 2-4 cm. Involucres 2-3 × 1.5-3 mm. Florets 3-9. Cypselae glabrous. 2n = 18, 36.

Flowering mid summer-late fall. Montane meadows, usually in rocky soils, sometimes in forested areas; 2000-2800 m; B.C.; Calif., Colo., Idaho, Mont., Nev., N.Dak., Oreg., S.Dak., Utah, Wash., Wyo.

Subspecies vaseyana is the common sagebrush of mountain slopes and is the most abundant of all the subspecies of Artemisia tridentata. A. A. Beetle (1960) estimated that it dominates an area of approximately 260,000 square kilometers. That estimate remains reasonably accurate today even though sagebrush is often cleared (by burning, herbicide spray, or the practice of `chaining´) and replaced by grasses (especially crested wheatgrass) suitable for livestock grazing. The acreage in which sagebrush has been removed appears to be more than compensated by acreage where it has increased in abundance because of overgrazing. While there may be evidence of introgression with other subspecies of A. tridentata, the subsp. vaseyana is usually well-separated geographically and ecologically from the other three subspecies. Variation within subsp. vaseyana may warrant the recognition of two varieties. A few-flowered (6 or fewer florets) form occurs at lower elevations (usually less than 2300 m) than the more robust form (with more than 6 florets per head), occurring at higher elevations (generally more than 2300 m). The type specimen of A. vaseyana is the large-headed variant. Pending further study, I am including var. pauciflora Winward & McArthur as part of subsp. vaseyana. In areas where populations of subsp. vaseyana co-occur with subspecies of A. cana, introgression is common.