49. Ranunculus glaberrimus Hooker, Fl. Bor.-Amer. 1: 12. 1829.
Stems prostrate or ascending, 4-15 cm, glabrous, each with 1-4 flowers. Roots cylindric, 1-3 mm thick. Basal leaves persistent, blades reniform or obovate to very narrowly elliptic, 0.7-5.2 × 1-2 cm, base truncate, obtuse or attenuate, margins entire or with 3 broad, apical crenae, apex rounded to acute. Flowers: pedicels glabrous or nearly so; receptacle glabrous; sepals 5-8 × 3-7 mm, abaxially glabrous or sparsely pilose, hairs colorless; petals 5-10, 8-13 × 5-12 mm; nectary scale glabrous or ciliate. Heads of achenes globose, 7-12(-20) × 6-11(-20) mm; achenes 1.4-2.2 × 1.1-1.8 mm, usually finely pubescent; beak subulate or lance-subulate, straight or curved, 0.4-1 mm.
Varieties 2 (2 in the flora): North America.
Usually only a minority of the ovaries develop, and the fruiting receptacle is completely hidden by aborted ovaries. Populations growing at high elevations ( Ranunculus glaberrimus var. ellipticus ) and low elevations (var. glaberrimus ) are usually well differentiated, but these varieties intergrade at intermediate elevations.
The Thompson Indians rubbed the flowers or the whole plant of Ranunculus glaberrimus on arrow points as a poison (D. E. Moerman 1986).