3. Sieversia Willdenow, Ges. Naturf. Freunde Berlin Mag. Neuesten Entdeck. Gesammten Naturk. 5: 397. 1811.
[For Johann August Carl Sievers, 1762–1795, German-born apothecary who explored eastern Russia in search of medicinal rhubarb]
Joseph R. Rohrer
Subshrubs (dwarf), ˂subscapose˃, 0.2–0.8[–1.5] dm; rhizomatous, ˂rhizomes branching, slender, woody; fibrous-rooted˃. Stems 1–5+, decumbent to ascending, simple, glabrous. Leaves deciduous, cauline (often crowded near stem apices), pinnately compound; stipules adnate to petiole base, linear, margins entire; petiole present; blade elliptic to obovate, 1–3.5 cm, herbaceous, leaflets 3–11, narrowly elliptic to obovate or rhombic, margins flat, entire or sharply lobed or toothed apically, venation pinnate, surfaces glabrous. Inflorescences terminal, flowers solitary; bracts 1 or 2. Pedicels present. Flowers 15–25 mm diam.; epicalyx bractlets 5; hypanthium saucer-shaped, 2 mm, puberulent; sepals 5, spreading, ovate; petals 5, white, some yellow at base or fading yellowish, obovate to elliptic; stamens 100–120, shorter than petals; torus hemispheric, ˂short-hairy˃; carpels 30–70, hairy, ˂styles not geniculate-jointed˃; ovule 1. Fruits aggregated achenes, 30–70, ovoid to fusiform, tapered apically, 2 mm, hairy; hypanthium persistent; sepals persistent, spreading to reflexed; styles persistent, elongating to 20[–27] mm, not hooked, ˂pilose except distal 1 mm˃. x = 7.
Species 1 or 2 (1 in the flora): Alaska, e Asia.
Sieversia is circumscribed here in its original narrow sense and follows the treatment by J. E. E. Smedmark (2006). Late nineteenth- and early twentieth-century authors often included within Sieversia all members of Colurieae with fruits bearing relatively long, slender, plumose styles that lack a geniculate joint. Smedmark and her colleagues have shown that this fruit type is probably ancestral in Colurieae and have argued for placement of all North American species, except for S. pentapetala, in Geum (see discussion under 4. Geum). The Asian endemic S. pusilla Hultén differs from S. pentapetala largely in its greater degree of blade division (the leaflets are deeply divided resulting in nearly bipinnate blades) and may or may not be a distinct species.