White-stem distaff thistle

Plants 30–100 cm, herbage glabrescent. Stems rigidly erect, shiny white, often much-branched distally. Leaves basal and cauline; basal often absent at anthesis, petioles winged. blades pinnately divided into 6–8 pairs of narrow lobes; cauline spreading or recurved, lanceolate to ovate, rigid, clasping, 3–7-veined from base, margins pinnately divided into 2–3 pairs of short, spine-tipped lobes, apices spine-tipped. Involucres ovoid, 10–13 mm, usually ± glabrous. Outer phyllaries ascending or ± spreading, very shiny, 40–50 mm, 2.5–3.5 times as long as inner, terminal appendages spreading to ascending, spiny-lobed, prominently spine-tipped. Corollas pink or pale purple, 13–17 mm, throats abruptly expanded; anthers white or pink with purple stripes; pollen white. Cypselae brown, 3–5 mm, outer roughened; pappus scales 5–7 mm. 2n = 20 (Greece).

Flowering summer (Jun–Aug). Disturbed sites; 0–200 m; introduced; Calif.; Europe (Greece, islands of Aegean Sea).

Between 1969 and 1990 an infestation of this noxious weed was documented in Sonoma County. Efforts to eradicate it were apparently successful.