Perennials, 200-300 cm (rhizomatous). Stems erect, glabrous (glaucous). Leaves cauline ; usually whorled (3s-6s), sometimes opposite; sessile or subsessile, petioles 0-1 cm; blades linear to lanceo-late, 7.5-18.5 × 0.7-3 cm, bases cuneate , margins serrulate or entire (flat), faces puberulent (abaxial) or hispid-strumose (adaxial), gland-dotted. Heads (1-)3-7+. Peduncles 1-10 cm. Involucres broadly campanulate, 15-20 mm diam. Phyllaries 45-55, lance-linear, 12-18 × 2-2.5 mm, (margins ciliate) apices long-attenuate, abaxial faces glabrate to sparsely puberulent, gland-dotted. Paleae 5-8 mm, entire or 3-toothed (apices ciliate). Ray florets 10-19; laminae 20-26 mm. Disc florets 150+; corollas 5-7 mm, lobes yellow; anthers dark, appendages yellow. Cypselae 4-5 mm, glabrous; pappi of 2 aristate scales 2.2-2.5 mm. 2n = 34. Flowering late summer-fall. Wet prairies; of conservation concern; 100-300 m; Ala., Ga., Tenn. Helianthus verticillatus is relatively uncommon and was recently rediscovered in scattered locations; it is a candidate for federal listing as an endangered species. It has been suggested to be a hybrid of H. angustifolius and H. eggertii or H. grosseserratus; no supporting evidence has been found to corroborate that suggestion.
This project made possible by National Science Foundation Award 1410069