Perennials, 40-60+ cm. Aerial nodes proximal to first peduncle usually 6-10+, distalmost 1-3 internodes 4-7+ cm. Leaves: mostly cauline on proximal 2/3-7/8 of plant heights; petioles 0 or 10-35+ mm; blades usually 1(-2)-irregularly pinnately or ± pedately lobed with (3-)5-9+ lobes, rarely simple, simple blades or terminal lobes narrowly lanceolate to linear or filiform, 15-45(-90+) × (0.5-)2-8(-12+) mm. Peduncles 8-15(-25+) cm. Calyculi of lanceolate to linear bractlets 3.5-9+ mm. Phyllaries lance-ovate, 7-9(-12) mm. Ray laminae yellow, 12-25+ mm. Disc corollas 3.3-4.8 mm, apices yellow. Cypselae 2-3+ mm, wings spreading, ± chartaceous, entire or irregularly toothed to pectinate. 2n = 26 (+ 0-2B).
Similar to no. 3 [Coreopsis lanceolata L.], occasionally annual, often taller (to 1 m), leafy nearly to the summit, the 1-many slender peduncles 0.5-2 dm, seldom more than half as long as the leafy part of the stem; lvs mostly pinnatifid into linear-filiform to narrowly lanceolate segments, the lateral lobes rarely more than 5 mm wide, the terminal one sometimes to 1 cm; outer bracts lance-subulate; rays averaging a little smaller; achenes often with a large callous ventral excrescence at top and bottom; 2n=26 + 0-4 B. Native to se. U.S., escaped from cult. and ±established in much of our range, especially southward. May, June. Ours is the widespread var. grandiflora.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.