This annual of the Old World tropics is a bad weed of rice fields. It has begun to spread through southern and western states during recent decades (Lipscomb 1980), and was discovered in Ky. at scattered roadsides and other disturbed sites during the 1990s (Mears & Libby 1995, Libby et al. 1997). This species has C3 photosynthesis, as in acuminatus and pseudovegetus also of Secton Pycnostachys; all other Cyperus in Ky. have C4 photosynthesis (Li et al. 1999).