Duration: Biennial

Nativity: Non-Native

Lifeform: Forb/Herb

General: Introduced biennial, 50-400 cm tall; stems erect, branched, appressed pubescent, spiny-winged; herbage grayish white tomentose; taprooted.

Leaves: Basal (usually absent by flowering) and cauline, alternate, broadly elliptic in outline, 10-60 cm long, 2- 15 cm wide, reduced upwards, densely tomentose, especially beneath, margins dentate to shallowly pinnatifid, spine-tipped; basal blades petiolate, cauline blades sessile and strongly winged-decurrent.

Flowers: Heads solitary or numerous, very showy, arranged in corymb- or panicle-like arrays; involucre cylindric, mostly 12-15 mm long; phyllaries 8-13 in 1-2 series, lanceolate to linear; ray flowers only, 18-50, blue; flowers June-September.

Fruits: Achene, 4-5 mm long, more-or-less cylindric, brown to gray-black, transversely roughened; pappus of numerous minutely barbed bristles, pink to reddish.

Ecology: Disturbed sites, roadsides, grasslands, woodlands; 900- 3000 m (3000-10000 ft); Apache, Coconino, Mohave, Navajo, and Yavapai counties; widespread throughout the U.S.

Notes: Ours, as here described, is ssp. acanthium. Onopordum acanthium is similar to Cirsium spp. but is distinguished by its fleshy and conspicuously honeycombed receptacle. Scotch thistle is a prohibited and restricted noxious weed in the state of Arizona.

Synonyms: - - -

Editor: Springer et al. 2008