Longleaf Sunflower

Helianthus longifolius is locally escaped from a planting in one county in North Carolina. It is locally abundant where it occurs. It is not similar to or closely related to any other species; natural hybrids of H. longifolius with H. atrorubens and H. occidentalis are known.

Perennials, 10–30 cm (with crown buds). Stems (green or purplish) erect, glabrous. Leaves mostly basal; opposite; petioles 0–1 cm; blades linear to narrowly obovate, 13–30 × 0.7–2 cm, bases cuneate, margins entire or obscurely serrate, faces glabrous, not gland-dotted (cauline smaller). Heads 3–12. Peduncles 4–11 cm. Involucres hemispheric, 8–12 mm diam. Phyllaries 18–23, linear-linear, 5–11 × 1–2.5 mm, (margins ciliolate) apices ± attenuate, abaxial faces glabrate or glabrous. Paleae 6–8 mm, weakly 3-toothed (apices hairy). Ray florets 8–13; laminae 10–19 mm (abaxial faces not gland-dotted). Disc florets 35+; corollas 4.2–5.5 mm, lobes yellow; anthers dark, appendages dark. Cypselae 2–3 mm, glabrate; pappi of 2 aristate scales 1.4–2.5 mm. 2n = 34.

Helianthus longifolius is a North American species of sunflower known by the common name longleaf sunflower. It is native to the southeastern United States (mostly Georgia and Alabama with one isolated population (probably introduced) in western North Carolina).

Helianthus longifolius is a perennial herb up to 30 cm (1 foot) tall. Most of the leaves are crowded around the base, each leaf up to 30 cm (1 foot) long. Leaves and stems generally have no hairs. One plant usually produces 3-12 flower heads. Each head has 8-13 yellow ray florets surrounding 35 or more yellow disc florets. The plant grows soils derived from sandstone and granite.