Key to Genera of the Subtribe Cenchrinae:

1. Inflorescence subtended by a spatheole…………………………………………………….2 1′. Inflorescence without a spatheole below…………………………………………………..4 2(1). Plants bisexual…………………………………………………………………..Xerochloa 2′. Plants dioecious……………………………………………………………………………….3 3. Male spikelets different from female ones; male inflorescence a single raceme…………………………………………………………………………….……....Spinifex 3′. Male spikelets similar to the female ones; male inflorescence similar to the female one……………………………………………………………………………………...Zygochloa 4(1′). Inflorescence composed of short racemes with spikelets embedded in a thickened central axis…………………………………………………………………………………Stenotaphrum 4′. Inflorescence without spikelets embedded in a thickened central axis…………………5 5(4′). Inflorescence composed of paired or digitate racemes…………………Stereochlaena 5′. Inflorescence open to contracted or spiciform, not composed of paired or digitate racemes……………………………………………………………………………………………6 6(5′). Spikelets with two fertile florets. Endemic of Hawaii…………………Dissochondrus 6′. Spikelets with a male, or neuter, floret below and a fertile floret apically (or male and female spikelets in different inflorescences)…………………………………………………..7 7(6′). Species with sexes segregated on unisexual branches; male spikelets above and female spikelets below………………………………………………………………………………....Hygrochloa 7′. Species without sexes segregated on unisexual branches………………………………...8 8(7′). Caryopsis with a linear hilum……………………………………………..Pseudoraphis 8′. Caryopsis with a punctiform to oblong hilum…………………………………………….9 9(8′). Inflorescence with disarticulation at maturity at the base of the primary branches or at the nodes of the inflorescence axis………………………………………………………………………………………………..10 9′. Inflorescence not disarticulating at the base of the primary branches…………………15 10(9). Lower palea winged, expanded at maturity. Africa…………………...Uranthoecium 10′. Lower palea not expanded at maturity. Australia……………………………………...11 11(10′). Lower glume developed, 3–7-nerved; upper glume ovate, 11–19-nerved (except Pseudochaetochloa, with upper glume 3-nerved and plants perennial); plants annual…...12 11′. Lower glume absent or obscure, nerveless; upper glume 0–7-nerved; plants perennial…………………………………………………………………………………………14 12(11). Upper glume 3-nerved; plants perennial………………………..Pseudochaetochloa 12′. Upper glume 11–19-nerved; plants annual……………………………………………...13 13(12′). Spikelets surrounded by a fan of bristles……………………………….Plagiosetum 13′. Bristle single…………………………………………………………………...Paractaenum 14(11′). Inflorescences of racemes in a bilateral false spike; lower glume linear, almost as long as the lower lemma, 7-nerved. Australia………………………………………………………………………..…Chamaeraphis 14′. Inflorescences of racemes in a multilateral false spike; lower glume reduce; nerveless. Africa and America………………………………………………………………………………..Paratheria 15(9′). Inflorescences without bristles………………………………………………………...16 15′. Inflorescences subtended with 1 to many bristles or spines…………………………...19 16(15). Spikelets laterally compressed………………………………………………………...............................................17 16′. Spikelets dorsiventrally compressed……………………………………………………..18 17(16). Ligule membranous-ciliate; inflorescence composed of unilateral racemes; upper glume and lower lemma 5–7-nerved; upper anthecium stipitate, rugose, and coriaceous…………………………………………………………………………...Whiteochloa 17′. Ligule ciliate; inflorescence with spikelets arranged in open, not racemose branches; upper glume and lower lemma 7–9-nerved; upper anthecium not stipitate, smooth, cartilaginous………………………………………………………………………….Alexfloydia 18(16′). Plants with the lowest internodes developed into a corm-like base, without strong rhizomes; internodes hollow; ligules membranous; upper anthecium rugose…………………………………………………………………………………..Zuloagaea 18′. Plants without corm-like bases, strongly rhizomatous; internodes solid; ligules membranous-ciliate; upper anthecium smooth…………………………………….Janochloa 19(15′). Bristles persistent on the inflorescence………………………………………………20 19′. Bristles or spines falling with the spikelets…………………………………………...…21 20(19). Lower palea expanded at maturity; C3 genus…………………………..Holcolemma 20′. Lower palea not expanded at maturity; C4 genus………………………………...Setaria 21(19′). Spikelet subtended by a single bristle………………………………………………22 21′. Spikelet surrounded by an involucre of bristles………………………………………...23 22(21). Panicle contracted, spiciform, first order branches appressed, short; lower palea not expanded at maturity…………………………………………………………………………….…Setariopsis 22′. Panicle open, first order branches divergent, long; lower palea expanded and winged at maturity………………………………………………………………………………...Ixophorus 23(21′). Inflorescence with distant racemes-like branches; leaf blades pseudopetiolate…………………………………………………………………...Streptolophus 23′. Inflorescence spiciform; leaf blades not pseudopetiolate……………………...Cenchrus