38. Ranunculus rhomboideus Goldie, Edinburgh J. Sci. 6: 329. 1822.
Stems erect, 5-22 cm, pilose or occasionally glabrous, each with 3-12 flowers. Roots slender, 0.8-1.8 mm thick. Basal leaves persistent, blades ovate to rhombic, undivided or rarely innermost 3-parted, 1.1-5.3 × 0.9-3.6 cm, base obtuse, margins crenate with 5 crenae, apex rounded. Flowers: pedicels pilose; receptacle pilose; sepals 4-6 × 1.5-3 mm, abaxially pilose, hairs colorless; petals 5, 6-8 × 2-4 mm; nectary scale glabrous. Heads of achenes depressed-globose, 4-6 × 5-7 mm; achenes 1.8-2.2 × 1.2-1.8 mm, glabrous; beak slender, curved, 0.2-0.3 mm. 2 n = 16.
Flowering spring (Apr-Jun). Prairies, or occasionally open woods or thickets; 0-900 m; Alta., B.C., Man., N.W.T., Ont., Sask.; Ill., Iowa, Mich., Minn., Mont., Nebr., N.Dak., S.Dak., Wis.
In addition to the range given above, L. D. Benson (1948) cited nineteenth-century specimens from Quebec, New York, Massachusetts, and Rhode Island. No modern specimens have been seen from those areas.