Nuttall, Trans. Amer. Philos. Soc., n. s. 7: 418. 1841.
Hooker's or white thistle
Biennials or monocarpic (sometimes polycarpic?) perennials
, 20—150 cm; taprooted.
usually 1 and erect, less commonly several and ascending, simple to sparingly short-branched in distal
/2, variably villous with jointed trichomes, and/or finely arachnoid, or ± glabrate; branches on distal stems 0—many, short, ascending.
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.
1—many, borne singly or crowded in spiciform, racemiform, subcapitate, or sometimes more openly branched corymbiform arrays.
(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.
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.
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.
dark brown, 5—6.5 mm, apical collars not differentiated;
Flowering summer (Jun—Sep). Moist soil, grasslands, aspen parkland, forest edges and openings, subalpine, alpine meadows; 600—2900 m; Alta., B.C.; Idaho, Mont., Wash., Wyo.
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
needs further investigation. A case could be made for including all three in an expanded concept of
, but more investigation of the variation patterns is needed before this is done. Certainly
is better treated within or as a close ally of
), where R. J. Moore and C. Frankton (1974) synonymized it.
is known to hybridize with