Plants annual. Stems erect, simple or branched, (6-)20-30(-60) cm; internodes glabrous or midstem ones slightly scabrous. Leaves: sheath 1-2 mm, ± as long as wide; blade 3-veined, linear to linear-lanceolate, 10-30 mm, margins serrate-scabrous. Inflorescences capitate; inflorescence bracts and involucel bracteoles enclosing flowers, broadly ovate, brown-scarious, apex obtuse or of outer bracts mucronate. Pedicels 0.1-1.5 mm. Flowers: sepals (7-)10-12 mm; petals pink to slightly purplish (rarely white), primary veins 1, veins not darkly colored near base of blade, apex truncate or emarginate. Seeds shield-shaped, 1.1-1.6(-1.8) mm, fine to coarsely reticulate. 2n = 30 (Europe). Flowering summer. Roadsides, ballast, fields; 0-1100 m; introduced; B.C.; Ala., Ark., Del., Ga., Idaho, Ky., Md., Mich., Mo., N.J., N.Y., N.C., Okla., Pa., Tenn., Va.; c, s Eurasia; introduced in Europe (Great Britain). Historical records for Petrorhagia prolifera exist also for California (1902; Congdon s.n., MIN), Ohio (last collected in 1896; Stair s.n., OS), and South Carolina (1800s; Durand s.n., NY).
Petrorhagia prolifera has been known in the northeastern United States since at least 1837, and its range has since expanded, with isolated populations occurring southwestward from New Jersey toward Arkansas and Oklahoma as well as western Michigan. Some introductions may have been as a contaminant in grass seed used for highway planting in Tennessee (B. E. Wofford et al. 1977). Literature reports of P. prolifera in Louisiana and West Virginia have not been confirmed.
Annual to 6 dm, simple or sparingly branched; internodes mostly glabrous; lvs linear or linear-oblong, 1-6 cm, to 2(-3) mm wide, 3-veined, scabrous-margined; fls in (1-)3-7-fld capitate cymes terminating the stem and branches, these, infls closely subtended by 2-3 pairs of large, scarious, brown, broadly ovate-oblong or obovate bracts forming an invol mostly 1-1.5 cm about equaling the fls, the fls also individually subtended by a pair of bracts; cal cylindric, 10-13 mm, 15-veined (5 veins the stronger); pet-blade short, pink, 1-veined, shallowly obcordate; seeds reticulate; 2n=30. European sp., cult. and sporadically escaped into disturbed sites in our range. May-Sept. (Tunica p.)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.