Dioecious perennial from a thick, scaly caudex; stems axillary to the caudex-scales, erect, 1-4 dm; lvs sessile, often somewhat glaucous, oblanceolate or obovate, 2-4 cm, entire or toothed toward the acute summit; infl compact, repeatedly branched, 1-5 cm wide; fls 4-merous or sometimes 5-merous, rarely 3-merous; pet oblanceolate to elliptic-oblong, 2-4.5 mm; follicles connivent, with short, spreading beaks. Cliffs and ledges; circumboreal, s. in the w. cordillera to Calif. and N.M., along the Atlantic coast to N.S. and Me., and disjunct inland in N.H., N.Y., Pa., N.C. to Tenn., and Minn. May-July. (Rhodiola r.) A complex, variable sp., here considered to consist of 2 major geographic phases that are morphologically ill-defined but cytologically apparently distinct. Var. rosea, with 2n=22, occurs in Atlantic N. Amer. and n. Eurasia; it has narrow pet (ca 1 mm wide or less) that are usually yellow or yellowish, sometimes red toward the tip. Var. integrifolium (Raf.) A. Berger, with 2n=36, is widespread in the w. cordillera, with outlying stations in the driftless area of se. Minn. and in c. N.Y. (where it adjoins the range of var. rosea); it has slightly wider pet (mostly 1-1.8 mm wide, but sometimes narrower) that are usually red or reddish, but sometimes largely yellow. (S. integrifolium; S. rosea var. leedyi)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.