Sunflowers are coarse annual or more commonly perennial herbs with simple leaves, the lowermost ones opposite, the others sometimes alternate. The flowerheads have rays, which are large, yellow, neutral. The involucral bracts are about equally arranged or sometimes evidently partly overlapping, generally green and more or less herb-like. The receptacle is flat to convex or low-cone-shaped, chaffy throughout, its bracts clasping the achenes. The disk flowers have both stamens and pistils and are fertile. The anthers are entire or minutely arrow-shaped at the base. The style branches are flattened, slightly bristly-hairy outside (and sometimes at the tip inside), with the short or elongate appendages slightly bristly-hairy on both sides. The marginal or inward-facing submarginal stigma-bearing lines are poorly developed. The achenes are thick, moderately flattened at right angles to the involucral bracts, with 2 evident and usually 2 obscure angles, generally hairless or nearly so. The pappus consists of 2 readily dropped awns with an enlarged thin, chaffy, translucent base (or they may be chaffy and translucent throughout), rarely having some additional short scales. The genus consists of about 60 species worldwide, native to the Americas. The name comes from the Greek helios, sun, and anthos, flower.
Guide to Identify Presented Species of Genus Helianthus
H. annuus Common Sunflower Coarse annual, 40-200 cm tall. Open, dry or moderately moist areas, roadsides.
Flowerheads several, large with yellow rays around a large button of disc florets.
Leaves alternate, egg- to heart-shaped with rough hairs and long stalks.