Swamp Sunflower

The distal parts of Helianthus angustifolius are identical in appearance to those of H. simulans; plants of the latter are taller (200+ cm) and more robust. The leaves are not only narrower in H. angustifolius but also tend to be more strongly revolute (abaxial faces sometimes scarcely visible).

Perennials, 50–150+ cm (with crown buds, rhizomes absent or poorly developed). Stems erect, usually ± hairy. Leaves mostly cauline; opposite or alternate; sessile or subsessile; blades (3-nerved near bases) narrowly lanceolate to linear, 8–15 × 0.15–0.5(–1) cm, bases cuneate , margins entire (revolute, abaxial face sometimes obscured by rolled margins), abaxial faces strigose to hispid or hirsute, sometimes (adaxial not) gland-dotted. Heads 3–16. Peduncles 5–15 cm. Involucres shallowly hemispheric, 10–20 mm diam. Phyllaries 25–32 (loose), lanceolate, 4–9 × 1–2 mm, apices acute to slightly acuminate, abaxial faces usually scabrous, rarely glabrous, usually gland-dotted. Paleae (oblanceolate) 5.5–6.5 mm, entire or ± 3-toothed (apices purplish, mucronate, gland-dotted). Ray florets 10–20; laminae 10–20 mm (abaxial faces gland-dotted). Disc florets 75+; corollas 4–4.5 mm, lobes yellow; anthers dark brown or black, appendages dark (style branches usually yellow). Cypselae 2–3 mm, glabrate; pappi of 2 aristate scales 1.5–2.1 mm. 2n = 34.

Helianthus angustifolius var. planifolius Fernald

Helianthus angustifolius is a species of sunflower known by the common name narrowleaf sunflower or swamp sunflower. It is native to the south-central and eastern United States, found in all the coastal states from Texas to Long Island, and inland as far as Missouri. It is typically found in the coastal plain habitat (both the Atlantic and Gulf), particularly in wet areas.

Helianthus angustifolius is often cultivated for its bright, showy yellow flowers. Leaves are long and narrow, up to 15 cm (6 inches) long. It is a perennial herb sometimes as much as 150 cm (5 feet) tall. One plant can produce 3-16 flower heads, each with 10-20 ray florets surrounding at least 75 disc florets.