Ranunculus hyperboreus

Stems prostrate, glabrous, rooting nodally. Leaves: basal leaves absent, cauline leaf blades reniform to broadly flabellate, deeply 3-lobed or 3-parted, 0.3-1.2 × 0.5-2.1 cm, base obtuse to cordate, lobes undivided or lateral lobes cleft, terminal segment entire or distally crenulate, apex rounded. Flowers: receptacle glabrous; sepals 3-4, spreading or reflexed from base, 2-4 × 1-3 mm, glabrous; petals 3-4, 2-4 × 1-3 mm; nectary on petal surface, scale poorly developed and forming crescent-shaped ridge surrounding but not covering nectary; style 0.1-0.2 mm. Heads of achenes globose or short-ovoid, 3-5 × 2-5 mm; achenes 1-1.4 × 0.8-1.2 mm, glabrous; beak linear, curved, 0.1-0.4 mm. 2 n = 32.

Flowering late spring-summer (Jun-Aug). Floating in shallow water or stranded on exposed mud at margins of streams and ponds and open wet soil and marshes, in tundra or boreal or subalpine forest; 0-3400 m; Greenland; Alta., B.C., Man., Nfld., N.W.T., Ont., Que., Sask., Yukon; Alaska, Colo., Idaho, Mont., Nev., Utah, Wyo.; Eurasia.

Specimens of Ranunculus hyperboreus from the central and southern Rocky Mountains have the leaves always cordate and the fruiting heads always 4-5 mm; they have been separated as R . hyperboreus subsp. intertextus . Although Arctic specimens are more variable, they often have shallowly cordate leaf bases and equally large heads of achenes, so segregation of the subspecies seems inappropriate.