11.
Cirsium horridulum
Michaux, Fl. Bor.-Amer. 2: 90. 1803.
Bristly or horrid or yellow or bull thistle
Biennials
or
perennials
, (± fleshy), 15—250 cm; stout taproots and a fascicle of fleshy lateral roots, often perennating by root sprouts.
Stems
1—several, usually erect, often stout, glabrous to densely tomentose; branches 0—many, spreading to ascending, short, stout.
Leaves
: blades linear to oblanceolate or oblong-elliptic, 10—40 × 2—10 cm, unlobed and spiny-dentate to deeply pinnatifid, lobes spiny-dentate or coarsely lobed, main spines stout, 5—30 mm, abaxial faces subglabrous to loosely tomentose, adaxial glabrous to ± densely villous with septate trichomes; basal present at flowering, spiny winged-petiolate, bases often tapered; principal cauline sessile, well distributed, often not much reduced distally, bases often ± auriculate-clasping; distal cauline often spinier than the proximal.
Heads
1—20 in subcapitate to corymbiform arrays (each closely subtended by an involucre-like ring of spiny-margined bracts).
Peduncles
0—5 cm.
Involucres
hemispheric to campanulate, 3—5 × 3—8 cm.
Phyllaries
in 5—9 series, subequal to imbricate, light green to stramineous, lanceolate to linear, distally often with reddish margins, abaxial faces without glutinous ridge, often ± thinly tomentose, often scabridulous in submarginal bands; outer and middle appressed-ascending, bodies usually reddish-tinged, margins setulose-ciliolate, apices acuminate, spines 1—2 mm, weak; apices of inner straight, flat.
Corollas
white to yellow, pink, purple, or red, 30—47 mm, tubes 11—30 mm, throats 6—10 mm, lobes 7—10 mm; style tips 3—5 mm.
Cypselae
straw-colored to tan, 4—6 mm, apical collars weakly differentiated;
pappi
25—35 mm.
2
n
= 32, 33, 34, 35.
Varieties 4 (3 in the flora): e United States, Mexico.
Although several variants have been given taxonomic recognition as species, these seem at most races. Flower color varies greatly, sometimes within populations and sometimes on a populational or regional basis. Herbarium specimens are sometimes difficult to assign to variety.
