Plants mostly dioecious. Rootstock erect or spreading, 0.5-2.5 cm diam. Floral stems deciduous, 5-40 × 0.2-0.6 cm. Leaf blades pale green, usually glaucous, ovate to obovate or oblong, 1-5 × 0.4-1.5 cm, margins entire or dentate, apex acute to obtuse. Inflorescences corymbose cymes, dense, to 150-flowered, to 6.5 cm diam. Pedicels ca. 3 mm. Flowers mostly unisexual, 4(-5)-merous; sepals linear-oblong or lanceolate, unequal, 1-2.5 mm; petals pale yellow to greenish yellow, sometimes red at tips, oblong, 1-3.5 mm, shorter than stamens, in staminate flowers spreading, hooded, 0.7-1.1 mm wide, in pistillate erect. Follicles 4-9 mm; beaks spreading. Seeds winged at both ends, pyriform, 1.7-2.2 mm. 2n = 22.

Flowering summer. Moist, rocky ledges and talus of coastal cliffs in the north and of north-facing cliffs; 0-1900 m; Greenland; St. Pierre and Miquelon; N.B., Nfld. and Labr., N.S., Que.; Alaska, Maine, N.Y., N.C., Pa., Vt.; Eurasia.

R. T. Clausen (1975) noted significant differences among wild populations of Rhodiola rosea [as Sedum rosea] but found that most lost significance when the plants were grown together at Ithaca. He found that staminate plants outnumber pistillate by about 1.2-1.9 to 1 and that an occasional plant has both staminate and pistillate flowers in the same cyme. From meiosis in staminate plants A. Levan (1933) reported one bivalent as slightly heteromorphic and possibly a sex-chromosome pair of the XY type, but C. H. Uhl (1952) noted no heteromorphic bivalents. Roseroot has a long history as a medicinal plant; Clausen summarized what was known of its chemistry and its uses. The name 'roseroot' is from the roselike odor of the dried rootstock.

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.

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