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FNA | Family List | FNA Vol. 19, 20 and 21 | Asteraceae | Cirsium

29b. Cirsium pulcherrimum (Rydberg) K. Schumann var. pulcherrimum

Wyoming thistle

Stems from branched or unbranched rootstocks, 15–60(–90) cm, bases often thickened. Adaxial leaf faces glabrous to thinly gray-tomentose. Heads often 4+, in ± elongate arrays. Cypselae often with stramineous apical collars. 2n = 34.

Flowering summer (Jun–Aug). Grasslands, sagebrush scrub, coniferous forest openings, roadsides, often in stony soil; 1100–2400 m; Colo., Idaho, Mont., Nebr., Utah, Wyo.

Variety pulcherrimum occurs from eastern Montana and northeastern Utah across Wyoming in the Wyoming Basin, Rocky Mountains, and western Great Plains to northern Colorado and northwestern Nebraska. It is likely that it occurs in southeastern Idaho as well. In the online Atlas of the Vascular Flora of Wyoming, several localities are plotted for var. pulcherrimum in Lincoln County, close to the Idaho state line. R. E. Brooks (1986) included Idaho in the range of C. pulcherrimum; I have not seen documentation for such occurrence. Cirsium pulcherrimum (i.e., var. pulcherrimum) is included in the list of Nebraska Plants of Special Concern.

Variety pulcherrimum is known to hybridize with Cirsium eatonii var. murdockii in Wyoming.


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