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 .
General: Perennial, 10-40 (70) cm tall; stems usually solitary, simple, base reddish, pubescence variable; stems separating easily from the roots. Leaves: Basal and cauline, mostly on the lower 1/4 of the stem, alternate, circular in outline, 1-6 cm long, 2-12 cm wide, nearly glabrous, lobes 5-12, 1-7 (14) mm wide (basal), 0.5-6 mm wide (cauline), the ultimate margins entire to lobed; petiole 0.4-12 cm long. Flowers: Inflorescence a raceme, 20-90 flowered, dense; pedicels ascending to spreading, 1-2 cm long, puberulent; flowers bilateral; sepals 5, dark blue to purple, puberulent, the lateral 2 spreading to slightly forward pointing, 10-14 mm long, the spur ascending or downcurved at the tip, 12- 15 mm long; petals 4, the lower ones slightly elevated and more-or-less exposing the stamens, white; pistils 3; flowers July-September. Fruits: Aggregate of follicles, 7-22 mm long, 3.5-5 times as long as wide; seeds numerous, dark brown, surfaces smooth or roughened. Ecology: Meadows, streambanks, ponderosa pine and mixed conifer forests, montane habitats; 1800-2600 m (6000-8500 ft); Apache, Coconino, Gila, Mohave, Navajo, and Yavapai counties; western United States. Notes: Delphinium scaposum (tall mountain larkspur) [=D. andersonii var. scaposum] is 25-60 (65) cm tall; stems are glabrous, glaucous; leaves are mostly basal, although sometimes a few cauline blades are present; the blades are circular in outline, 0.5-4 cm long, 0.5-6 cm wide, glabrous to puberulent, with 3-9 lobes; racemes are mostly 10-25 flowered, sometimes more; sepals are bright dark blue, glabrous; and the fruit is 12-16 mm long, 2.5- 3 times longer than wide. It mostly occurs in pinyon- juniper woodlands and grasslands, but is known to occur within our range. Editor: Springer et al. 2008