Longdisk Sneezeweed

Helenium quadridentatum is introduced in Pennsylvania.

Annuals, 30–100 cm. Stems usually 1, branched distally, moderately to strongly winged, glabrous or sparsely hairy. Leaves glabrous or sparsely hairy; blades narrowly elliptic to lance-linear, usually entire; proximal blades sometimes pinnately lobed. Heads 5–15(–50+) per plant, in paniculiform arrays. Peduncles 3–13 cm, sparsely to moderately hairy. Involucres ovoid to conic, 7–11(–14) × 6–11 mm. Phyllaries (connate proximally) sparsely to densely hairy. Ray florets 10–15, pistillate, fertile; corollas yellow, 7–12.4 × 4–8.8 mm. Disc florets 225–500+; corollas yellow proximally, yellow to brown to reddish brown distally, 1.1–1.8 mm, lobes 4. Cypselae 0.6–1.2 mm, moderately hairy; pappi of usually 6 entire, non-aristate scales 0.1–0.3 mm. 2n = 26.

Helenium quadridentatum Labill. Act. Soc. Hist. Xat. Paris
1: 22. 1792.
Rudbeckia alata Jacq. Ic. PI. Rar. 3: 16. 1793.
Helenia linearifolia Moench, Meth. Suppl. 240. 1802.
Helenium alatum C. C. Gmel. Hort. Carlsr. 129. 1811.
Mesodetra alata Raf. Fl. Ludov. 141. IS 17.
? Helenium quadripartitum Link, Knum. 2: 338. 1822.
Helenium Miller i Schultes; DC. Prodr. S: 566, as svnonym. 1836.
? Helenium discovatum Raf. New Fl. 4: 81. 1838.
Heleniastrum quadridentatum Kuntze, Rev. Gen. 342. 1891.
A paniculately branched annual or biennial; stem 3-10 dm. high, glabrous or sparingly puberulent; lower leaves elliptic, oblanceolate, or oblong, pinnately lobed, about 1 dm. long; upper leaves entire, lanceolate or linear-lanceolate, acute or acuminate, decurrent into the wings of the stem; peduncles 5-8 cm. long; involucre about 1 cm. broad; bracts narrowly linear or subulate, soon reflexed; receptacle oblong; ligules yellow, broadly cuneate, 3-5 mm. long; disk oblong, at least in fruit, 8-10 mm. broad, 10-15 mm. long; corollas little more than 1 mm. long; tube a minute ring; throat campanulate; limb usually 4-toothed; achenes about 1 mm. long, hispidulous on the angles; pappus of minute rounded squamellae.
Type locality: Louisiana; described from cultivated plants.
Distribution: South Carolina to Florida, Texas, Vera Cruz, and Yucatan; Martinique.

Helenium quadridentatum is a North American plant in the sunflower family, commonly known as longdisk sneezeweed. It is found in the southeastern and south-central United States (Alabama, Mississippi, Louisiana, Texas, Oklahoma) as well as Mexico (from Tamaulipas to Yucatán), Cuba, Guatemala, and Belize.

Helenium quadridentatum is an annual herb up to 100 cm (39.5 in) tall, with small wings running down the sides of the stems. Leaves are sometimes broadly elliptical, other times very narrow and grass-like. One plant generally produces up to 50 flower heads, in a branching array. Each head has an egg-shaped or conical disc containing can have 500 or more minuscule disc flowers each 1.1–1.8 mm (0.043–0.071 in) across, each yellow toward the bottom but yellow-brown toward the tip. There are also 10-15 yellow ray flowers.