Delphinium pauciflorum Nuttall in J. Torrey & A. Gray, Fl. N. Amer. 1: 33. 1838, not D. pauciflorum D. Don 1825, not D. pauciflorum Reichenbach ex Chamisso 1831; D. nuttallianum var. fulvum C. L. Hitchcock; D. nuttallianum var. levicaule C. L. Hitchcock; D. sonnei Greene

Stems unbranched, 10-40(-70) cm; base reddish, pubescence variable. Leaves mostly on proximal 1/4 of stem; basal leaves 2-6 at anthesis; cauline leaves 2-10 at anthesis; petiole 0.4-12 cm. Leaf blade round, 1-6 × 2-12 cm, nearly glabrous; ultimate lobes 5-21, 5 or more extending more than 3/5 distance to petiole, width 1-7(-14) mm (basal), 0.5-6 mm (cauline), widest at middle or in proximal 1/2. Inflorescences 4-18(-48)-flowered, at least 2 times as long as wide; pedicel 0.8-6 cm, pubescence variable; bracteoles 3-8(-18) mm from flowers, green to blue, linear, 3-7 mm, pubescence variable. Flowers: sepals usually bluish purple, rarely white to pink, puberulent, lateral sepals reflexed or spreading, 8-21 × 3-10 mm, spurs decurved to straight, ascending 20-60° above horizontal, 8-23 mm; lower petal blades elevated, exposing stamens, blue to purple, except sometimes in white-flowered plants, 4-11 mm, clefts 2-5 mm; hairs mostly on inner lobes below junction of blade and claw, white, rarely yellow. Fruits 7-22 mm, 3.5-5 times longer than wide, glabrous to puberulent. Seeds winged or not; seed coat cell surfaces smooth or roughened, blunt hairs absent. 2 n = 16.

Flowering spring (-early summer). Open coniferous woods, grassy sage scrub, meadow edges and well drained streamsides (generally not in very wet sites); 300-3500 m; B.C.; Ariz., Calif., Colo., Idaho, Mont., Nev., N.Mex., Oreg., Utah, Wash., Wyo.

Delphinium nuttallianum represents an extremely difficult complex, with many variations in a number of morphologic traits. The complex has been and continues to be a major source of confusion for identification of Delphinium in North America. Type specimens of D . nuttallianum represent plants growing under dry conditions in open areas. These are typically found at 1200-2000 m in sage scrub or lower montane forest. Delphinium nuttallianum may be confused with D . andersonii , D . antoninum , D . depauperatum , D . gracilentum , and two subspecies of D . patens (subsp. patens and subsp. montanum ). Features that may be used to separate D . nuttallianum from the first four, are enumerated under the respective species discussions. From D . patens subsp. patens , D . nuttallianum may be distinguished by its narrower leaf lobes, larger fruits, and more compact inflorescence. The frequent presence of glandular hairs in the inflorescence of D . patens subsp. montanum , contrasted with their absence in D . nuttallianum , will separate these taxa. Dwarfed plants of D . polycladon may be confused with D . nuttallianum . The latter, however may be distinguished by its ringed seeds, and it does not have prominent buds or sigmoid pedicel.

Hybrids have been seen between Delphinium nuttallianum and D . andersonii , D . depauperatum ( D . × burkei Greene), D . distichum ( D . × diversicolor Rydberg), D . nudicaule , and D . polycladon .