Plants annual. Stems erect, simple or branched, (20-)30(-52) cm; internodes glabrous or midstem and proximal ones minutely stipitate-glandular. Leaves: sheath (2-)3-4 mm, 1.5-2 times as long as wide; blade 3-veined, linear, 10-25 mm, margins scabrous. Inflorescences capitate; inflorescence bracts and involucel bracteoles enclosing flowers, broadly ovate, brown-scarious, apex of outer bracts mucronate, of inner bracts obtuse or mucronate. Pedicels 0.1-2 mm. Flowers: sepals (5-)10-12 mm; petals pink to slightly purplish, primary veins 3, at least center vein darkly colored near base of blade, apex obcordate or 2-fid. Seeds shield-shaped, (1.3-)1.5-1.8 mm, tuberculate. 2n = 60 (Europe).

Flowering late spring-summer. Roadsides; 0-200 m.; introduced; B.C.; Calif.; w Europe; nw Africa; introduced in South America, Australia.

Petrorhagia nanteuilii is known from two counties in northern California (first collected in 1956) and a single site in British Columbia. It may be an alloploid derived through hybridization between P. prolifera and P. dubia; recent attempts at crossing the latter two have failed (S. M. Thomas and B. G. Murray 1983).