This pantropical annual (or short-lived perennial) of seasonally wet sites extends north to temperate regions of North America. Variation needs further assessment. Much material from Ky. with relatively small reddish-brown spikelets has been referred to C. ferruginescens Boeck., which was formerly segregated in eastern and central states by F and others. However, ferruginescens is generally not recognized in recent treatments, even as a variety (FNA 23). Typical odoratus (= C. ferax L.), in its narrow sense, is a relatively southern taxon, but present in Ky. as well. See also notes under engelmannii. C. odoratus is sometimes confused with erythrorhizos in the field, since both species have brown to reddish scales. Subgenus Diclidium (with odoratus) differs from subgenus Cyperus (with erythrorhizos) as follows (FNA 23, W): rachilla corky-thickened, transversely articulated at the base of each scale (versus not so), the spikelets at maturity separating into 1-fruited dispersal units with the scale persistent (versus persistent or deciduous), the rachilla segment and wings conspicuously clasping the achene, the spikelets visibly "jointed" at maturity and breaking apart (versus not so); spikelets linear and terete, the scale tips slightly spreading (versus ovoid to linear, compressed, quadrangular or terete).