Stems 20-60 cm; base often reddish, nearly glabrous. Leaves mostly on proximal 1/3 of stem; basal leaves 0-4 at anthesis; cauline leaves 2-8 at anthesis; petiole 4-12 cm. Leaf blade round, 2-8 × 4-12 cm, nearly glabrous; ultimate lobes 3-18, 5 or more extending more than 3/5 distance to petiole, width 2-10 mm (basal), 4-10 mm (cauline), widest at middle or in proximal 1/2. Inflorescences 5-15(-30)-flowered, less than 3 times longer than wide; pedicel 1-2.5 cm, puberulent; bracteoles 1-4(-6) mm from flowers, green, linear, 3-5 mm, puberulent. Flowers: sepals deep bluish purple to pink or white, puberulent, lateral sepals spreading, 11-19 × 4-7 mm, spurs straight, within 30° of horizontal, 13-16 mm; lower petal blades ± covering stamens, blue, except sometimes in white-flowered plants, 6-10 mm, clefts 0.5-2 mm; hairs sparse, mostly centered near junction of blade and claw, white. Fruits 14-22 mm, 4-4.5 times longer than wide, nearly glabrous. Seeds unwinged; surface of each seed coat cell with 1-5 small, swollen, elongate, blunt, hairlike structures, barely visible at 20× otherwise smooth. 2 n = 16. Flowering spring. Slopes in deciduous forests, thicket edges, moist prairies; 10-1500 m; Ala., Ark., D.C., Ga., Ill., Ind., Iowa, Kans., Ky., Md., Miss., Mo., Nebr., N.C., Ohio, Okla., Pa., S.C., Tenn., Va., W.Va. Delphinium tricorne is the most commonly encountered larkspur east of the Great Plains. The Cherokee prepared infusions of Delphinium tricorne to ingest for heart problems, although they believed the roots of the plant made cows drunk and killed them (D. E. Moerman 1986).
From Flora of Indiana (1940) by Charles C. Deam
Infrequent to frequent in rich soil on wooded slopes in the southern counties, becoming less frequent northward and probably very local or entirely absent from the northern two tiers of counties. It seems to have very little affinity for streams, because it is usually found near the bases of slopes of ravines as well as along streams. This wild species is easily cultivated in the garden. I have a specimen which I collected on May 1, 1910, in a woods near Wilson Creek northwest of Lawrenceburg, in Dearborn County, on which I have the following note: "In this station I estimate that there is an average of 1 plant for every square foot of space over an area of 20 acres of woodland." I have seen it in large colonies but usually only a few plants are found at a station. The plant is poisonous to stock. I met a farmer who lived a mile north of Cedar Grove in Franklin County who called the plant stagger weed and told me that he had known cattle to be killed by eating it.
Plants 2-6 dm, from a cluster of short, tuberous roots; lvs few, mostly at or near the base, deeply divided into several oblong-linear or cuneate segments; raceme 8-20 cm, softly short-villous, the pedicels 1-3 cm, the fls few, blue or sometimes white; spur 12-18 mm; lateral sep 11-15 mm, lower pet not bifid; follicles 10-15 mm, divergent; seeds smooth, triangular. Rich, moist woods; Pa. to s. Minn., s. to N.C., Ga., Ala., and Okla. Apr., May.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.