Helianthus hirsutus Rafin.

Helianthus hirsutus is distinguished from H. strumosus by hairy stems and usually yellow (as opposed to dark) anther appendages, and from H. divaricatus by petioles and leaf blades 3-nerved distal to bases. Mexican plants of H. hirsutus are sometimes labeled with the synonymous H. leptocaulis (S. Watson) S. F. Blake, and plants from Mexico and the southwestern United States often have leaf bases cuneate rather than truncate.

Perennials, 100–200 cm (rhi-zomatous). Stems erect, hirsute. Leaves cauline; mostly opposite; petioles 0.4–2 cm; blades (3-nerved from bases) lanceolate to ovate, 6.5–18 × 1–8 cm, bases truncate to broadly rounded or cuneate, margins subentire to serrate (flat), abaxial faces ± hirsute, gland-dotted (adaxial not gland-dotted). Heads 1–7. Peduncles 1–5 cm. Involucres hemispheric, 10–25 mm diam. Phyllaries 18–25 (usually loose, spreading, not reflexed), lanceolate, 7–12 × 2.5–3.5 mm, (margins ciliate) apices acute to short-acuminate, abaxial faces not gland-dotted. Paleae 7–10 mm, 3-toothed (apices yellowish, hairy). Ray florets 10–15; laminae 15–20 mm. Disc florets 40+; corollas 5.5–6.5 mm, lobes yellow; anthers dark brown or black, appendages dark or yellowish. Cypselae 4–4.5 mm, glabrate or distally puberulent; pappi of 2 aristate scales 2.5–3.2 mm. 2n = 68.

Helianthus hirsutus var. stenophyllus Torrey & A. Gray; H. hirsutus var. trachyphyllus Torrey & A. Gray; H. stenophyllus (Torrey & A. Gray) E. Watson

Helianthus hirsutus is a North American species of sunflower known by the common name hairy sunflower. It is widespread across south-central Canada, the eastern and central United States, and northeastern Mexico. It ranges from Ontario south to Florida, Coahuila, and Nuevo León, and west as far as Minnesota, Nebraska, and Texas.

Helianthus hirsutus is a perennial sometimes as much as 200 cm (almost 7 feet) tall, spreading by means of underground rhizomes. Leaves and stems are covered with stiff hairs. One plant can produce 1–7 flower heads, each with 10–15 yellow ray florets surrounding 40 or more yellow disc florets. The species grows in sunny locations in open forests or along the edges of forests.

Helianthus hirsutus là một loài thực vật có hoa trong họ Cúc. Loài này được Raf. mô tả khoa học đầu tiên năm 1820.