Paspalidium Fl. Trop. Afr. 9: 582 (1920).
Derivation:. Latin analogy of Paspalum.
Taxonomic revisions, nomenclatural references:. R.D.Webster, Sida 16:439–442 (1995) (Paspalidium placed in synonymy with Setaria)..
Key references (keys and floras):. C.A.Gardner, Flora of Western Australia 1 Gramineae 246–250 (1952); E.E.Henty, Manual Grasses New Guinea 143–144 (1969); J.W.Vickery, Flora of New South Wales, Gramineae 19: 138–155 (1975); M.Lazarides, Tropical Grasses S.E. Asia 131 (1980); M.Lazarides, Flora of Central Australia 478–479 (1981); J.C.Tothill and J.B.Hacker, Grasses of Southern Queensland 328–331 (1983); J.P.Jessop, Flora of South Australia 4: 1971–1972 (1986); R.D.Webster, Australian Paniceae 151–169 (1987); T.D.Macfarlane, Flora of the Kimberley Region 1199–1299, 1202 (1992); B.K.Simon, Key to Australian Grasses 139–140 (1993); S.W.L.Jacobs and C.A.Wall, Flora of New South Wales 4: 477–481 (1993); N.G.Walsh, Flora of Victoria 2: 603–604 (1994); D.Sharp and B.K.Simon, AusGrass (2002); S.W.L.Jacobs, R.D.B.Whalley & D.J.B.Wheeler, Grasses of New South Wales, 4th ed, 320–325 (2008).
W.D.Clayton & S.A.Renvoize, Genera Graminum (1986), genus (504).
Native. About 40 species, from warm regions. 22 species in Australia, WA, NT, SA, Qld, NSW, and Vic. Also New Guinea and Malesia.
Habit. Annual or perennial (often aquatic), rhizomatous or tufted to decumbent. Leaf blades broad or narrow. Ligule a fringed membrane (very narrow) or a fringe of hairs.
Inflorescence. Inflorescence of spicate main branches to a false spike, with spikelets on contracted axes (the branches generally appressed to the rachis, and sometimes greatly reduced), a single raceme or spike or a racemose panicle with spikelets all similar. Spikelet-bearing axes racemes or much reduced.
Spikelets. Spikelets dorsally compressed, 2 flowered, with 1 fertile floret, with raceme axis extending into a bristle, unaccompanied by bractiform involucres, not associated with setiform vestigial branches, solitary or paired. Fertile spikelets with lower incomplete floret(s), elliptic or lanceolate or ovate, abaxial (with lower glume on side away from rachis), falling with glumes.
Glumes. Glumes unequal, (the upper) about equal to spikelet, (the upper) shorter than adjacent lemmas or long relative to adjacent lemmas, awnless, non-keeled. Lower glume 1–5 nerved. Upper glume 5–11 nerved.
Florets. Lower incomplete floret(s) male, or sterile. Lemmas resembling the upper glume, awnless, more or less equalling fertile lemmas, less firm than fertile lemmas, not becoming indurated (membranous). Fertile florets 1. Lemmas decidedly firmer than glumes, rugose, becoming indurated (crustaceous), yellow in fruit or brown in fruit, entire at apex, pointed, muticous (often apiculate), with a clear germination flap, 5 nerved, glabrous, having margins tucked into palea. Palea relatively long, entire, firm, like the lemma, 2 nerved. Lodicules 2. Stamens 3. Grain small, ellipsoid to subglobose, compressed dorsiventrally. Hilum short. Embryo large.
Kranz Anatomy. C4.
2n = 18, 36, and 54, 2, 4, and 6 ploid.
Habitat. Hydrophytic to mesophytic. Swamps, forests, dry slopes. Shade species and species of open habitats.
Classification. Panicoideae; Paniceae.
Notes. Typically the genus has distant racemes with neatly imbricate spikelets, which seem very different from Setaria. In fact the gap is bridged by intermediate species with looser racemes so that the diagnostic criterion -most of the spikelets lacking bristles- is rather arbitrary, though seldom difficult to apply. The rachis tip is easily overlooked and the genus can then be confused with Urochloa or Panicum (Clayton and Renvoize, 1986). Some agrostologists (Veldkamp, 1994; Webster, 1995) maintain that because there is a continuum in variation of the bristle arrangement between Paspalidium and Setaria, the generic separation is difficult to apply, and they place all species of Paspalidium under Setaria (B.K.Simon).
Types Species. P. geminatum (Forssk.) Stapf.
Biogeographic Element. Clifford & Simon 1981, Simon & Jacobs 1990: Gondwanan.