Pennisetum is closely related to the genus Cenchrus, and the boundary between them is unclear.Cenchrus was derived from Pennisetum and the two are grouped in a monophyleticclade. Some species now in Pennisetum were once members of Cenchrus, and some have been moved back. A main morphological character used to distinguish them is the degree of fusion of the bristles in the inflorescence, but this is often unreliable. Authors recently proposed to transfer Pennisetum into Cenchrus, along with the related genus Odontelytrum.
They are annual or perennial grasses. Some are petite while others can produce stems up to 8 meters tall. The inflorescence is a very dense, narrow panicle containing fascicles of spikelets interspersed with bristles. There are three kinds of bristle, and some species have all three, while others do not. Some bristles are coated in hairs, sometimes long, showy, plumelike hairs that inspired the genus name, the Latinpenna ("feather") and seta ("bristle").
Annuals or perennials. Inflorescence a cylindric to subspherical, spike-like panicle, bearing deciduous clusters of 1-several spikelets subtended by an involucre of bristles, these flexuous, filiform and free to base. Spikelets: glumes and lower lemma variable, 0 to as long as spikelet; upper lemma cartilaginous to thinly coriaceous with flat thin margins.
Barcode of Life Data Systems (BOLD) Stats Specimen Records:70 Specimens with Sequences:94 Specimens with Barcodes:71 Species:19 Species With Barcodes:17 Public Records:14 Public Species:5 Public BINs:0