Thurber’s sneezeweed

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.