Smallhead Sneezeweed

Annuals, 25–120 cm. Stems 1(2–10), branched distally, moderately to strongly winged, glabrous or sparsely hairy. Leaves glabrous or sparsely to moderately hairy (basal withered by flowering); proximal and mid blades narrowly elliptic to narrowly oblong-elliptic, usually serrate to undulate-serrate, sometimes deeply toothed or laciniate; distal blades narrowly elliptic to narrowly oblong-elliptic, serrate to undulate-serrate. Heads 20–300+ per plant, in paniculiform arrays. Peduncles 1.8–8 cm, moderately hairy. Involucres globoid to usually ovoid, 4–12 × 4–12 mm. Phyllaries (connate proximally) moderately hairy. Ray florets 7–13, pistillate, fertile; corollas usually yellow throughout, sometimes reddish proximally and yellow distally, 2.6–9.1 × 1.5–6.7 mm. Disc florets 120–400+; corollas yellow to yellow-green proximally, brown to reddish brown distally, 1.2–2.4 mm, lobes (4–)5. Cypselae 0.7–1.4 mm, moderately hairy; pappi of usually 6 entire, non-aristate scales (0.2–)0.3–0.7 mm.

Helenium microcephalum is a North American perennial plant in the sunflower family, commonly known as smallhead sneezeweed. It is found in the southwestern and south-central United States and northern Mexico.

Helenium microcephalum is an annual herb up to 120 cm (3.9 ft) tall, with wings running down the sides of the stems. Leaves are narrow and elliptical. One plant can have 300 or more small spherical or egg-shaped flower heads, generally no more than 12 mm (half an inch) in diameter. Each head can have 400 or more minuscule disc flowers 1.2–2.4 mm (0.047–0.094 in) across, each yellow or yellow-green toward the bottom but brown or red toward the tip. There are also 7-13 red or yellow ray flowers.

Varieties Helenium microcephalum var. microcephalum - Arizona, New Mexico, Oklahoma, Colorado, Texas, Coahuila, Nuevo León, Tamaulipas Helenium microcephalum var. ooclinium (A. Gray) Bierner - Texas, Coahuila, Chihuahua, Nuevo León, Durango, San Luis Potosí