Stems 50–120(–150) cm, usually thorny proximally but armament of distal portions variable among populations, some producing only thornless, wandlike branches. Leaves mostly 10–40 mm. Involucres 4–5.5(–6) mm. Ray floret laminae 3.5–5(–7) mm. 2n = 18.

Flowering (May–)Aug–Nov. Riverbanks, freshwater swamps, bottomlands, low prairies, saline flats, ditches, irrigation channels; 0–1200(–1500) m; Ariz., Calif., La., Nev., N.Mex., Okla., Tex., Utah; Mexico.