69. Potentilla hyparctica Malte, Rhodora. 36: 177. 1934.
Arctic cinquefoil
Potentilla robbinsiana (Lehmann) Oakes ex Rydberg subsp. hyparctica (Malte) D. Löve
Plants cushion-forming; caudex branches short to elongate, slender, ˂often embedded in old leaf bases˃. Stems ascending to erect, 0.2–2(–2.5) dm, lengths 1–3(–4) times basal leaves. Basal leaves not in ranks, ternate, (1–)2–8(–10) cm; stipules: apex ± acute; petiole 1–6.5(–8.5) cm, long hairs sparse to common, spreading to subappressed, 0.8–2 mm, weak to ± stiff, glands sparse to common; leaflets 3, central obovate to broadly obovate, 0.5–2.5(–2.8) × 0.3–2(–2.2) cm, petiolule 0–3 mm, margins flat or slightly revolute, not lobed, distal 1/2–2/3(–3/4) evenly incised ± 1/2 to midvein, teeth (2–)3–5 per side, surfaces ± similar, abaxial usually pale green, sometimes grayish, hairs sparse to abundant, 0.5–1.7 mm, adaxial darker green, hairs and glands sparse. Inflorescences 1–3(–5)-flowered. Pedicels straight, 0.3–3 cm in flower, to 9 cm in fruit. Flowers: epicalyx bractlets narrowly to broadly oblong or ovate, 3.5–7 × 1.5–5 mm, margins flat; hypanthium 4–7 mm diam.; sepals 4–8 mm, apex subacute to rounded; petals pale or bright yellow, 4–9 × 4–6 mm; filaments 0.5–1.1 mm, anthers 0.2–0.4 mm; carpels 50–80, styles ± columnar, not or scarcely papillate-swollen proximally, 0.6–0.9 mm. Achenes 1.1–1.3 mm.
Subspecies 3 (2 in the flora): North America, n Eurasia; circumpolar.
Southern arctic and subarctic plants differ from the northern arctic ones in presumably independent features. Where the two forms are sympatric (western Greenland, northern Quebec, Baffin Island), they appear to remain distinct even in mixed populations and are accordingly treated as subspecies.
Although some features of scattered plants in Alaska and Yukon approach subsp. nivicola Jurtzev & V. V. Petrovsky (described from northeastern Asia), such plants do not otherwise correspond fully with this taxon. Possible hybrids between Potentilla hyparctica and P. pulchella (sect. Pensylvanicae) are addressed in the discussion of sect. Pensylvanicae. Presumed hybrids with P. villosa from the Aleutian Islands, characterized by the combination of basally thickened styles and lack of cottony hairs on leaflet abaxial surfaces, have been named P. ×aleutica Soják.
