48. Delphinium luteum A. Heller, Bull. S. Calif. Acad. Sci. 6: 68. 1903.
Stems 20-40(-55) cm; base often reddish, nearly glabrous. Leaves mostly on proximal 1/4 of stem; basal leaves 4-9 at anthesis; cauline leaves 2-4 at anthesis; petiole 0.5-6 cm. Leaf blade round to pentagonal, 1-5 × 2-10 cm, nearly glabrous; ultimate lobes 3-5, width 8-30 mm (basal), 5-15 mm (cauline). Inflorescences 5-25(-37)-flowered; pedicel (1-)3-5(-7) cm, puberulent; bracteoles 6-10(-17) mm from flowers, green, linear-lanceolate, 6-7 mm, nearly glabrous. Flowers: sepals bright yellow, puberulent, appearing waxy, lateral sepals ± forward pointing, (11-)14-16 × (6-)9-13 mm, spur straight, ca. 30° below horizontal, 11-20 mm; lower petal blades elevated, exposing stamens, 3-4 mm, clefts 0.5-1.5 mm; hairs sparse or absent, ± evenly distributed if present, white to yellow. Fruits 11-14 mm, 3.5-4.5 times longer than wide, glabrous. Seeds unwinged; seed coat cell surfaces smooth.
Flowering late winter-mid spring. Wet cliffs, coastal grassland or chaparral; of conservation concern; 0-50 m; Calif.
Delphinium luteum is presently known from only three populations. It is known to hybridize with D . decorum and with D . nudicaule . Populations of D . hesperium subsp. hesperium also occur at the type locality; D . luteum flowers earlier and hybrids are not known.
Delphinium luteum is not likely to be mistaken for any other species of Delphinium . It has been treated as a variety of D . nudicaule and is closely related to that species. Sepals of the infrequent yellow-flowered phase of D . nudicaule , however, have a much drabber appearance compared with the bright shining yellow of the sepals in D . luteum .