Cirsium pulcherrimum |
Cirsium pulcherrimum var. pulcherrimum |
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Wyoming thistle |
Wyoming thistle |
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Habit | Perennials polycarpic, 15–60(–90) cm; deep-seated woody tap-roots and caudices. | |||||
Stems | 1–few, erect or ascending, arachnoid-tomentose or ± glabrate; branches 0–5+, usually in distal 1/2, ascending. |
from branched or unbranched rootstocks, 15–60(–90) cm, bases often thickened. |
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Leaves | blades linear to oblong, oblanceolate, or elliptic, 5–25 × 0.6–7 cm, unlobed and merely spinulose or spiny-dentate to regularly pinnatifid, lobes 5–8(–many) pairs, well separated, usually with broad, U-shaped sinuses to crowded, linear to triangular-ovate, ascending-spreading to retrorse, merely spinulose to coarsely dentate or few lobed, main spines 2–7 mm, ± slender, abaxial faces gray to white, usually densely arachnoid-tomentose, sometimes ± glabrate, sometimes villous with septate trichomes along veins, adaxial green, glabrous or less commonly thinly to densely gray-tomentose; basal often present at flowering, spiny winged-petiolate; principal cauline well distributed, gradually reduced distally, proximal usually winged-petiolate, mid and distal sessile, bases decurrent as spiny wings 1.5–3.5 cm; distalmost reduced, ± bractlike. |
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Peduncles | 0–15 cm. |
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Involucres | ovoid to campanulate, 1.8–2.7 × 1–2 cm, thinly arachnoid-tomentose or glabrate. |
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Corollas | pink to purple (creamy white), 18–25 mm, tubes 7–9 mm, throats 5.5–7.5 mm, lobes 4–8 mm; style tips 3–5.5 mm. |
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Phyllaries | in 6–7 series, ± imbricate, green or with dark subapical patch or appendage, linear to linear-lanceolate, margins entire, abaxial faces with narrow glutinous ridge; outer and middle bases appressed, apical appendages spreading to stiffly ascending, linear-lanceolate to acicular, entire, spines spreading or ascending, stout, 2–7 mm, often flattened; apices of inner stiffly erect or sometimes flexuous, narrow, flat. |
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Heads | 1–few, borne singly or in 2–3-headed clusters in ± congested flat-topped or racemiform arrays at tips of main stem and branches, sometimes also in distal axils. |
often 4+, in ± elongate arrays. |
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Cypselae | tan to dark brown, 5–6 mm, apical collars yellow, narrow; pappi 14–16 mm. |
often with stramineous apical collars. |
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Adaxial | leaf faces glabrous to thinly gray-tomentose. |
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2n | = 34. |
= 34. |
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Cirsium pulcherrimum |
Cirsium pulcherrimum var. pulcherrimum |
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Phenology | Flowering summer (Jun–Aug). | |||||
Habitat | Grasslands, sagebrush scrub, coniferous forest openings, roadsides, often in stony soil | |||||
Elevation | 1100–2400 m (3600–7900 ft) | |||||
Distribution |
CO; ID; MT; NE; UT; WY
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CO; ID; MT; NE; UT; WY |
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Discussion | Varieties 2 (2 in the flora). Cirsium pulcherrimum is closely related to C. clavatum. In southeastern Wyoming and northern Colorado some plants combine foliage and involucral characters of C. pulcherrimum var. pulcherrimum and C. clavatum var. americanum. The inheritance of these characters needs to be examined at the population level to determine whether the intermediates are hybrids or the products of past introgression or incomplete differentiation. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 19, p. 125. | FNA vol. 19, p. 126. | ||||
Parent taxa | Asteraceae > tribe Cardueae > Cirsium | Asteraceae > tribe Cardueae > Cirsium > Cirsium pulcherrimum | ||||
Sibling taxa | ||||||
Subordinate taxa | ||||||
Synonyms | Carduus pulcherrimus | |||||
Name authority | (Rydberg) K. Schumann: Just’s Bot. Jahresber. 29(1): 566. (1903) | unknown | ||||
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