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.