1. Caltha leptosepala de Candolle, Syst. Nat. 1: 310. 1817.
Caltha biflora de Candolle; C. biflora subsp. howellii (Huth) Abrams; C. biflora var. rotundifolia (Huth) C. L. Hitchcock; C. howellii (Huth) Greene; C. leptosepala var. rotundifolia Huth; C.leptosepala var. sulfurea C. L. Hitchcock; C. uniflora Rydberg; Psychropila leptosepala (de Candolle) W. Weber
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 **
C . leptosepala C . bicolor
in strict sense in strict sense
Leaf (L:W ratio) 0.8-2.2(-3.1) 0.4-1.5
Flower number 2-4 1-4
Stipe (mm) 0-3.2 0-2.7 *Including Alaska, Arizona, Colorado, Idaho, and Montana.
**Including British Columbia, California, Oregon, and Washington.
Morris, M. I. 1973. A biosystematic analysis of the Caltha leptosepala (Ranunculaceae) complex in the Rocky Mountains. III. Variability in seed and gross morphological characters. Canad. J. Bot. 51: 2259-2268. Smit, P. G. and W. Punt. 1969. Taxonomy and pollen morphology of the Caltha leptosepala complex. Proc. Kon. Ned. Akad. Wetensch. C. 72: 16-27.