Stems leafless or with 1 leaf, erect. Basal leaves: blade oblong-ovate to orbiculate-reniform, largest 1.5-11.5(-15) × 1-13cm, margins entire or crenate to dentate. Inflorescences 1-2(-4)-flowered. Flowers 15-40 mm diam.; sepals white to yellow (abaxially bluish), 8.5-23 mm. Follicles 4-15, spreading, short-stipitate or sessile, linear-oblong; bodies 10-20 × 3-4.5 mm; style and stigma straight or curved, 0.5-1.8 mm. Seeds elliptic, 1.9-2.5 mm. 2 n =48,96.
Flowering late spring-summer (Jun-Aug). Open, wet, subalpine and alpine marshes, wet seepages; 750-3900 m; Alta., B.C., Yukon; Alaska, Ariz., Calif., Colo., Idaho, Mont., Nev., N.Mex., Oreg., Utah, Wash., Wyo.
Caltha leptosepala is morphologically complex, and a number of segregate taxa have been described. Plants are most commonly assigned to two species, however. Caltha leptosepala in strict sense is found in the Rocky Mountains of Arizona and New Mexico north to Alaska and is characterized by longer-than-broad leaves with small, nonoverlapping basal lobes, solitary-flowered inflorescences, and sessile follicles. Plants in the Coast Ranges of central California north to the coastal islands of southern Alaska, distinguished by broader-than-long leaves with large, overlapping basal lobes, 2-flowered inflorescences, and stipitate follicles, have been called C . biflora . My comparison of specimens from the Rocky Mountains and the Coast Ranges indicated that no clear distinction could be made (table 1). While plants are often distinctive in the southern part of their range, a continuous intergradation between the two extremes exists over much of their range.
Table 1. Morphologic comparison of Caltha leptosepala from the Rocky Mountains and Coast Ranges. Rocky Mountains * Coast Ranges **
**Including British Columbia, California, Oregon, and Washington.
General: Perennial, 5-30 cm tall; stems erect, scapose or with 1 leaf; stolons slender; roots fibrous. Leaves: Basal, seldom with 1 cauline blade, oblong-ovate to nearly orbicular, 1.5-11.5 cm long, 1-13 cm wide, glabrous, margins entire or crenate to dentate, base cordate, apex rounded; petiole 2-22 cm long. Flowers: Inflorescence a cyme of few to several flowers; bracts subtending the inflorescence leaf-like, similar in shape to the leaflets; flowers radial, nodding; sepals elliptic-ovate, ovate, or lanceolate, 0.7-2 cm long, red, the apex sometimes yellowish green; petal spurs 1.6-3.2 cm long, slender, red, blades oblong or rounded, 4-12 mm long, yellow, or red and yellow; stamens 1.4-1.9 cm long; flowers June-October. Fruits: Aggregate of follicles, linear-oblong, the body 1-2 cm long, style and stigma straight or curved, 0.5-1.8 mm long; seeds several, elliptic. Ecology: Wet meadows, seeps, springs, marshes, and other wet areas in alpine and subalpine habitats; 2300-3400 m (7500-11000 ft); Apache, Coconino, Graham, and Greenlee counties; western Canada, western and southwestern U.S. Notes: This plant can appear similar vegetatively to Ranunculus spp. with cordate basal leaves, but these all have well- defined stems and variously shaped stem leaves, whereas C. leptosepala is strictly scapose. Editor: Springer et al. 2008