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Wyoming thistle

cobwebby thistle, snowy thistle, Venus thistle, western thistle

Habit Perennials polycarpic, 15–60(–90) cm; deep-seated woody tap-roots and caudices. Biennials, 5–400 cm; taproots.
Stems

1–few, erect or ascending, arachnoid-tomentose or ± glabrate;

branches 0–5+, usually in distal 1/2, ascending.

usually 1, thinly to densely gray- or white-tomentose, sometimes ± glabrate;

branches few–many, usually from above mid or near base in compact, moundlike dwarf plants, ascending to spreading.

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.

blades oblong–elliptic to oblanceolate, 6–40 × 1.5–10+ cm, shallowly to deeply pinnatifid, lobes usually rigidly spreading, undivided or with 1–2 pairs of coarse teeth or lobes, main spines 5–15 mm, both faces gray- to white-tomentose, sometimes ± glabrate or adaxial faces green, thinly arachnoid-tomentose;

basal sometimes present at flowering, petiolate or sessile and bases tapered, spiny-winged;

principal cauline much reduced distally, sessile, bases decurrent or not, as spiny wings;

distal much reduced, linear, ± bractlike.

Peduncles

0–15 cm.

1–30 cm.

Involucres

ovoid to campanulate, 1.8–2.7 × 1–2 cm, thinly arachnoid-tomentose or glabrate.

ovoid to spheric, 1.5–5 × 1.5–8 cm, arachnoid to ± loosely tomentose, often adjacent phyllaries connected by conspicuous arachnoid trichomes, sometimes glabrous or glabrate.

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.

white to lavender, pink, rose-purple, or red, 18–40 mm, tubes 8–18 mm, throats 5–7 mm, lobes 5–10 mm;

style tips 4–5 mm.

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.

in 7–10 series, subequal to strongly imbricate, green or stramineous to purple-tinged, linear to narrowly lanceolate, abaxial faces without glutinous ridge;

outer and mid bodies appressed, entire, apices deflexed to spreading or ascending, short-triangular to elongate, linear-acicular, spines spreading to reflexed, 1–10+ mm;

apices of inner erect, often flexuous, flat.

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.

1–many in loose to tight clusters (barely raised above rosette in dwarf plants).

Cypselae

tan to dark brown, 5–6 mm, apical collars yellow, narrow;

pappi 14–16 mm.

± brown, 5–6 mm, apical collars not differentiated;

pappi 15–30 mm.

2n

= 34.

Cirsium pulcherrimum

Cirsium occidentale

Distribution
from FNA
CO; ID; MT; NE; UT; WY
[WildflowerSearch map]
[BONAP county map]
from FNA
CA; NV; OR
[WildflowerSearch map]
[BONAP county map]
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.)

Varieties 7 (7 in the flora).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Key
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
1. Plants compact, rounded, moundlike; heads usually not much elevated above leaves
var. compactum
1. Plants usually erect; principal heads usually conspicuously pedunculate
→ 2
2. Corollas white to light purple or rose
var. californicum
2. Corollas deep purple to bright pink or red
→ 3
3. Plants densely white-tomentose; phyllaries persistently white-tomentose (except spines); outer phyllaries usually very long, spreading to reflexed
var. candidissimum
3. Plants variably tomentose, sometimes ± glabrate; phyllaries ± arachnoid to floccose-tomentose, sometimes green and glabrate; outer phyllaries short to long, ascending to spreading or reflexed
→ 4
4. Involucres usually about as long as wide or wider than long; phyllaries densely and persistently arachnoid with fine trichomes connecting tips of adjacent phyllaries
→ 5
4. Involucres usually longer than wide; phyllaries tomentose or glabrate, sparingly or not arachnoid with fine trichomes connecting tips of adjacent phyllaries
→ 6
5. Phyllary apices ± imbricate, the proximal usually shorter than medial and distal, lanceolate to linear-acicular, 0.5–15 mm; co- rollas bright purple
var. occidentale
5. Phyllary apices subequal, all long- acicular, 1.5–3 cm; corollas light to deep reddish purple
var. coulteri
6. Corollas 20–24 mm, deep reddish purple; s Santa Lucia Mountains of San Luis Obispo County, California
var. lucianum
6. Corollas 23–35 mm, bright pink to red; widespread
var. venustum
Source FNA vol. 19, p. 125. FNA vol. 19, p. 137.
Parent taxa Asteraceae > tribe Cardueae > Cirsium Asteraceae > tribe Cardueae > Cirsium
Sibling taxa
C. altissimum, C. andersonii, C. andrewsii, C. arizonicum, C. arvense, C. barnebyi, C. brevifolium, C. brevistylum, C. canescens, C. carolinianum, C. ciliolatum, C. clavatum, C. crassicaule, C. cymosum, C. discolor, C. douglasii, C. drummondii, C. eatonii, C. edule, C. engelmannii, C. flodmanii, C. foliosum, C. fontinale, C. grahamii, C. helenioides, C. hookerianum, C. horridulum, C. hydrophilum, C. inamoenum, C. joannae, C. kamtschaticum, C. lecontei, C. longistylum, C. mohavense, C. muticum, C. neomexicanum, C. nuttallii, C. occidentale, C. ochrocentrum, C. ownbeyi, C. palustre, C. parryi, C. perplexans, C. pitcheri, C. praeteriens, C. pumilum, C. quercetorum, C. remotifolium, C. repandum, C. rhothophilum, C. rydbergii, C. scariosum, C. texanum, C. tracyi, C. turneri, C. undulatum, C. vinaceum, C. virginianum, C. vulgare, C. wheeleri, C. wrightii
C. altissimum, C. andersonii, C. andrewsii, C. arizonicum, C. arvense, C. barnebyi, C. brevifolium, C. brevistylum, C. canescens, C. carolinianum, C. ciliolatum, C. clavatum, C. crassicaule, C. cymosum, C. discolor, C. douglasii, C. drummondii, C. eatonii, C. edule, C. engelmannii, C. flodmanii, C. foliosum, C. fontinale, C. grahamii, C. helenioides, C. hookerianum, C. horridulum, C. hydrophilum, C. inamoenum, C. joannae, C. kamtschaticum, C. lecontei, C. longistylum, C. mohavense, C. muticum, C. neomexicanum, C. nuttallii, C. ochrocentrum, C. ownbeyi, C. palustre, C. parryi, C. perplexans, C. pitcheri, C. praeteriens, C. pulcherrimum, C. pumilum, C. quercetorum, C. remotifolium, C. repandum, C. rhothophilum, C. rydbergii, C. scariosum, C. texanum, C. tracyi, C. turneri, C. undulatum, C. vinaceum, C. virginianum, C. vulgare, C. wheeleri, C. wrightii
Subordinate taxa
C. pulcherrimum var. aridum, C. pulcherrimum var. pulcherrimum
C. occidentale var. californicum, C. occidentale var. candidissimum, C. occidentale var. compactum, C. occidentale var. coulteri, C. occidentale var. lucianum, C. occidentale var. occidentale, C. occidentale var. venustum
Synonyms Carduus pulcherrimus Carduus occidentalis
Name authority (Rydberg) K. Schumann: Just’s Bot. Jahresber. 29(1): 566. (1903) (Nuttall) Jepson: Fl. W. Calif., 509. (1901)
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