Cirsium hookerianum |
Cirsium occidentale |
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Hooker's thistle, white thistle |
cobwebby thistle, snowy thistle, Venus thistle, western thistle |
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Habit | Biennials or monocarpic (sometimes polycarpic?) perennials, 20–150 cm; taprooted. | Biennials, 5–400 cm; taproots. | ||||||||||||||||||||||||
Stems | usually 1 and erect, less commonly several and ascending, simple to sparingly short-branched in distal 1/2, variably villous with jointed trichomes, and/or finely arachnoid, or ± glabrate; branches on distal stems 0–many, short, 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. |
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Leaves | blades linear-oblong to elliptic, 5–25 × 1–8 cm, subentire to coarsely dentate or deeply pinnatifid, lobes lance-oblong to broadly triangular, spinulose to spiny-dentate or shallowly lobed, main spines 2–10 mm, abaxial faces usually ± densely gray- or white-tomentose with felted arachnoid trichomes, ± villous to tomentose along major veins with septate trichomes, sometimes glabrous or glabrate, adaxial ± green, glabrous to thinly arachnoid, often ± villous or tomentose with septate trichomes; basal often present at flowering, spiny winged-petiolate or sessile; principal cauline well distributed, proximally winged-petiolate, distally sessile, gradually reduced, bases sometimes short-decurrent; distal ± reduced, often narrower than proximal, sometimes with non-pigmented bases, sometimes pectinately spiny. |
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. |
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Peduncles | 0–8+ cm. |
1–30 cm. |
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Involucres | (green or often purplish), broadly ovoid, 2–3.3 × 1.5–4 cm, loosely to densely villous with septate trichomes to tomentose and/or arachnoid. |
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. |
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Corollas | white, ochroleucous, or occasionally pink, 20–28 mm, tubes 10–13 mm, throats 6.5–9 mm, lobes 5–7 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. |
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Phyllaries | in 4–8 series, imbricate to subequal, bases short-appressed, entire, abaxial faces with or without narrow glutinous ridge, apices stiffly spreading to ascending, linear, long, plane, spines straight, slender, 3–5 mm; apices of inner flexuous, sometimes expanded and erose. |
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. |
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Heads | 1–many, borne singly or crowded in spiciform, racemiform, subcapitate, or sometimes more openly branched corymbiform arrays. |
1–many in loose to tight clusters (barely raised above rosette in dwarf plants). |
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Cypselae | dark brown, 5–6.5 mm, apical collars not differentiated; pappi 18–22 mm. |
± brown, 5–6 mm, apical collars not differentiated; pappi 15–30 mm. |
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2n | = 34. |
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Cirsium hookerianum |
Cirsium occidentale |
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Phenology | Flowering summer (Jun–Sep). | |||||||||||||||||||||||||
Habitat | Moist soil, grasslands, aspen parkland, forest edges and openings, subalpine, alpine meadows | |||||||||||||||||||||||||
Elevation | 600–2900 m (2000–9500 ft) | |||||||||||||||||||||||||
Distribution |
ID; MT; WA; WY; AB; BC
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CA; NV; OR
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Discussion | Cirsium hookerianum occurs from the Canadian Coast Ranges of British Columbia east to the northern Cascade Range and the northern Rocky Mountains. The relationship between C. hookerianum, C. kelseyi, which I have tentatively included in C. hookerianum, and C. longistylum needs further investigation. A case could be made for including all three in an expanded concept of C. hookerianum, but more investigation of the variation patterns is needed before this is done. Certainly C. kelseyi is better treated within or as a close ally of C. hookerianum than in C. scariosum (var. scariosum), where R. J. Moore and C. Frankton (1974) synonymized it. Cirsium hookerianum is known to hybridize with C. undulatum. (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.) |
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Key |
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Source | FNA vol. 19, p. 148. | FNA vol. 19, p. 137. | ||||||||||||||||||||||||
Parent taxa | Asteraceae > tribe Cardueae > Cirsium | Asteraceae > tribe Cardueae > Cirsium | ||||||||||||||||||||||||
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Synonyms | C. kelseyi | Carduus occidentalis | ||||||||||||||||||||||||
Name authority | Nuttall: Trans. Amer. Philos. Soc., n. s. 7: 418. (1841) | (Nuttall) Jepson: Fl. W. Calif., 509. (1901) | ||||||||||||||||||||||||
Web links |