Typically, these areas are subject to scouring floods. It also known from a single site in Arkansas, on the Cossatot River, and in isolated populations along the Obed River on the Cumberland Plateau of Tennessee. Purpletop can be distinguished from Cumberland sandreed by a denser, drooping, inflorescence. Also, the culms, panicle branches and spikelets of purpletop are covered with a sticky, odorous substance. Purpletop has ventrally compressed spikelets, but differs from Cumberland sandreed by having two glumes and four to eight fertile florets.
Caryopses fall from purpletop without the glume, as they do in Cumberland sandreed.
The persistence of Cumberland sandreed is dependent upon freely flowing streams. Several populations of Cumberland sandreed have been lost to permanent flooding of habitat as a result of reservoir construction. Heavy grazing along stream banks may also result in the decline of Cumberland sandreed populations. Recovery Needs Careful management of riparian zones, including forested buffer strips, is an important strategy for protection of this species. Physical alteration of river banks, sand bars, and natural streamflow should be avoided.