Annuals, 40-100 cm. Stems usually 1, branched distally, moderately winged, sparsely hairy proximally, moderately hairy distally. Leaves glabrous or sparsely hairy (basal leaves withered by flowering); proximal blades lanceolate to lance-linear, usually irregularly laciniate; mid and distal blades lance-linear, entire. Heads 10-75(-120+) per plant, in paniculiform arrays. Peduncles 3-10 cm, moderately hairy. Involucres ovoid to conic, 6-10 × 5-10 mm. Phyllaries (strongly connate proximally), moderately hairy. Ray florets 0. Disc florets 225-500+; corollas yellow-green proximally, brown to reddish brown distally, 1-1.3 mm, lobes 4. Cypselae 0.9-1.2(-1.5) mm, moderately hairy; pappi of 6(-7) entire, non-aristate scales 0.2-0.5 mm. 2n = 26.
Flowering (Mar-)May-Jul(-Sep). Ditches, around ponds, along streams, moist fields; 30-1600 m; Ariz.; Mexico.
Wiggins 1964, FNA 2006, Kearney and Peebles 1969
Duration: Annual Nativity: Native Lifeform: Forb/Herb General: Ascending, much branched annual 40-100 cm tall, stems slender, puberulent, obviously winged, sparsely hairy near the base, moderately hairy above. Leaves: Lower oblanceolate, 5-15 cm long, more or less puberulent, subentire to sharply dentate, upper leaves lanceolate to lance-linear, 2-7 cm long, entire. Flowers: Heads on slender peduncles 3-10 cm long, striate, heads 10-75 per plant, in paniculiform arrays, discoid, broadly ovoid to subglobose, 5-12 mm in diameter with linear involucral bracts 3-7 mm long, slightly hirsutulous, corollas greenish yellow, faintly tinged with purplish or brownish at tips of lobes, about 1 mm long; no ray florets, 225-500+ disc florets. Fruits: Cypselae about 1 mm long moderately hairy with pappi of 6 entire, non-aristate scales. Ecology: Found in marshy places along streams, in moist disturbed sites from 100-5,500 ft (31-1676 m); flowers April-October. Distribution: s AZ; south to c MEX. Notes: Distinguished by the winged stems and heads with lack of rays and many, many disc florets. Ethnobotany: Unknown Etymology: Helenium is thought to be named for Helen of Troy by Linnaeus, while thurberi is named for Dr. George Thurber (1821-1890) a botanist on the Mexican Boundary Survey of 1850-1854. Synonyms: None Editor: SBuckley 2010, FSCoburn 2015