This is a widespread variable weed of eastern North America, with a great range in overall stature; 2n = 36 and 54 (FNA 25). A coll. from BALL (MUR) is referable to var. geniculata (Wood) Fern., with less erect stems and less exerted panicles (F), but that taxon has not been recognized in recent treatments. A coll. from JACK (EKY) has been referred to var. puritanorum Svens., which was considered a somewhat distinct subspecies in FNA 25, with relatively small spikelets. Var. puritanorum is typical of receding shorelines in northeastern regions. Further research is needed to determine the status of these potential segregates in Ky. Leaves have a distinctive whitish zone along the midvein.