Potentille des deux mondes

Potentilla multifida Linnaeus subsp. bimundorum (Soják) Soják

Stems decumbent to ascending, rarely erect, 1–5 dm. Basal leaves subpinnate, 7–22(–25) cm; petiole 3–12(–15) cm, long hairs ± abundant, appressed to ascending, 0.5–3 mm, stiff, short hairs absent, cottony or crisped hairs absent, glands absent or sparse; leaflets 3(–4) per side, on distal 1/5–1/3(–1/2) of leaf axis, overlapping or not, terminal ones oblong to broadly oblong, 1.5–5 × 0.7–2 cm, margins strongly revolute, incised nearly to midvein, undivided medial blade 1–3 mm wide, teeth (3–)4–5 per side, linear, rarely narrowly oblong to narrowly lanceolate, surfaces strongly dissimilar, abaxial white or grayish white, long hairs abundant, ± 1 mm, stiff ˂verrucose˃ on veins, sparse and soft between veins, short hairs absent, crisped and cottony hairs dense, glands absent, adaxial dark green, long hairs sparse to common, tightly appressed, 0.5–1 mm, short hairs absent, cottony and crisped hairs absent, glands absent or sparse. Cauline leaves (1–)2–3. Inflorescences (5–)10–40+-flowered, ± congested to open. Pedicels 0.3–1 cm (proximal to 3 cm). Flowers: epicalyx bractlets linear to narrowly oblong-lanceolate, 3–5 × 0.9–1.3 mm, lengths ± 3/4 times sepals, margins flat; hypanthium 2.5–3.5 mm diam.; sepals 4–7(–8) mm, apex acute to obtuse, abaxial surfaces: venation prominent at least proximally, glands ± sparse, obscured to evident; petals pale yellow, 3.5–5 × 3–5 mm, lengths ± equal to sepals; filaments 0.5–1.5 mm, anthers 0.5–0.6 mm; carpels 40–60, styles papillate-swollen at very base, if at all, 0.8–0.9 mm. Achenes 1.3–1.5 mm, rugose. 2n = 28.

Flowering summer. Road and railway verges, gravelly ruderal sites, acidic rocky outcrops, stream banks and gravel bars, sandy-gravelly flood plains, gravel ridges, sandy lakeshores, sandy steppe bluffs; 0–1000 m; Alta., Man., N.W.T., Nunavut, Ont., Que., Sask., Yukon; Alaska; e Asia (Russian Far East).

Potentilla bimundorum is the correct name for what has been treated as P. multifida Linnaeus in North America. It is the only American representative of the mainly Eurasian P. multifida group, which is sometimes treated as a distinct section. J. Soják (2005) presented a useful survey and key to this group, showing that its species, in spite of being merged within P. multifida in the broad sense by many authors, are each distinct and with their own range. Potentilla multifida in the narrow sense is restricted to eastern Europe and western Siberia.