5. Thelesperma megapotamicum (Sprengel) Kuntze, Revis. Gen. Pl. 3(2): 182. 1898.
Bidens megapotamica Sprengel, Syst. Veg. 3: 454. 1826; Thelesperma gracile (Torrey) A. Gray
Perennials or subshrubs, (20–)30–80+ cm. Cauline leaves ± scattered over proximal 1/2–3/4 of plant heights, internodes mostly 40–100 mm; lobes mostly linear to filiform, sometimes oblanceolate, 20–40(–50+) × 0.5–1(–2.5) mm. Calyculi of 3–5+ ovate to oblong bractlets 1–2(–3) mm. Ray florets 0. Disc corollas yellow, often with red-brown nerves, throats shorter than lobes. Cypselae 5–8 mm; pappi 1–2(–3) mm. 2n = 22, 44.
Flowering (Apr–)May–Oct. Disturbed places on sands or clays, oak/juniper woodlands, desert scrub, yellow-pine forests; 300–2900 m; Ariz., Ark., Colo., Kans., Nebr., N.Mex., Okla., S.Dak.. Tex., Utah, Wyo.; Mexico (Chihuahua, Coahuila); South America.
Thelesperma megapotamicum sometimes persists after plantings outside its natural range in the flora area and may become established (e.g., in California).