Annuals, 100-300 cm. Stems erect, usually hispid. Leaves mostly cauline; mostly alternate; petioles 2-20 cm; blades lance-ovate to ovate, 10-40 × 5-40 cm, bases cuneate to subcordate or cordate, margins serrate, abaxial faces usually ± hispid, sometimes gland-dotted . Heads 1-9. Peduncles 2-20 cm. Involucres hemispheric or broader, 15-40(-200+) mm diam. Phyllaries 20-30(-100+), ovate to lance-ovate, 13-25 × (3-)5-8 mm, (margins usually ciliate) apices abruptly narrowed, long-acuminate, abaxial faces usually hirsute to hispid, rarely glabrate or glabrous, usually gland-dotted. Paleae 9-11 mm, 3-toothed (middle teeth long-acuminate, glabrous or hispid). Ray florets (13-)17-30(-100+); laminae 25-50 mm. Disc florets 150+(-1000+); corollas 5-8 mm (throats ± bulbous at bases), lobes usually reddish, sometimes yellow ; anthers brownish to black, appendages yellow or dark (style branches yellow) . Cypselae (3-)4-5(-15) mm, glabrate ; pappi of 2 lanceolate scales 2-3.5 mm plus 0-4 obtuse scales 0.5-1 mm. 2n = 34. Flowering summer-fall. Open areas; 0-3000 m; St. Pierre and Miquelon; Alta., B.C., Man., N.B., N.W.T., N.S., Ont ., P.E.I., Que., Sask.; Ala., Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; Mexico; intoduced nearly worldwide. Helianthus annuus is widely distributed, including weedy, cultivated, and escaped plants. It is the only native North American species to become a major agronomic crop. Despite its considerable variability, attempts have failed to produce a widely adopted infraspecific system of classification. Forms with red-colored ray laminae, known from cultivation and occasionally seen escaped, trace their ancestry to a single original mutant plant. It hybridizes with many of the other annual species.

Plant: Robust annual forb to 3 m in moist areas; stems erect, ± rough-hairy Leaves: leaves opposite below, alternate above, scabrous, deltoid, petiolate, long-petioled; blade 10-40 cm, base generally ± cordate, tip obtuse to acute, margin serrate INFLORESCENCE: primary inflorescence a head, each resembling a flower; heads generally few-many; peduncles 2-20 cm; involucre 1.5-3(20) cm diam; phyllaries 15-25 mm, lanceolate to widely ovate, abruptly acuminate, glabrous to rough-hairy, generally ciliate; chaff scales deeply 3-lobed, middle lobe long-acuminate Flowers: Ray flowers 15-many, sterile; ligule generally > 2.5 cm, yellow; Disk flowers: many, corollas 5-8 mm, lobes red to purple or yellow, tube short, throat base often swollen, lobes triangular; style appendages triangular Fruit: achenes, 3-15 mm, oblanceolate to obovate, ± compressed; sides rounded; pappus scales 2-3.5 mm Misc: Disturbed areas, scrub, many other habitats; < 1900 m.; Jul-Oct References: J.C. Hickman, ed. The Jepson Manual.W.D. McDougal. Seed plants of Northern Arizona. ASU specimens.