Cirsium pulcherrimum
Cirsium pulcherrimum var. aridum
Wyoming thistle
Cedar Rim thistle
1–few, erect or ascending, arachnoid-tomentose or ± glabrate;
branches 0–5+, usually in distal 1/2, ascending.
often clustered from branched rootstock, 15–40 cm, bases not thickened.
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.
0–15 cm.
ovoid to campanulate, 1.8–2.7 × 1–2 cm, thinly arachnoid-tomentose or glabrate.
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.
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.
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.
1–4, in compact arrays.
tan to dark brown, 5–6 mm, apical collars yellow, narrow;
pappi 14–16 mm.
without stramineous apical collars.
leaf faces gray- to white-tomentose.
= 34.
Cirsium pulcherrimum
Cirsium pulcherrimum var. aridum
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.)
Of conservation concern.
In describing variety aridum, Dorn suggested that it “seems to belong to the C. hookerianum group,” but I fail to see this relationship. Its affinities clearly lie with Cirsium pulcherrimum. It is usually differentiable from var. pulcherrimum by the characters above, but it grows and intergrades with var. pulcherrimum on the Sweetwater Plateau in Fremont County. W. Fertig (unpubl.) has studied the ecology and distribution of var. aridum [as C. aridum] and the very similar pubescent forms of var. pulcherriumum [as C. pulcherrimum].
Variety aridum occurs in scattered localities on barren hills in Carbon, Fremont, and Sweetwater counties. It is a rare taxon, but it has not received official recognition by governmental agencies. However it is in the Center for Plant Conservation’s National Collection of Endangered Plants.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Distal leaf face gray- to white-tomentose; cypselae without stramineous apical collar | var. aridum |
1. Distal leaf face usually green, glabrous or ± glabrate, but sometimes persistently tomentose; cypselae often with narrow stramineous apical collar | var. pulcherrimum |
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