Hymenachne Essai Agrost. 48, 165 (1812).
Derivation:. From Greek hymen (membrane) and achne (glume), referring to the nature of the glumes.
Key references (keys and floras):. E.E.Henty, Manual Grasses New Guinea 109 (1969); M.Lazarides, Tropical Grasses S.E. Asia 122 (1980); J.C.Tothill and J.B.Hacker, Grasses of Southern Queensland 272–273 (1983); R.D.Webster, Australian Paniceae 99–100 (1987); B.K.Simon, Key to Australian Grasses 125 (1993); 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, 280–281 (2008).
W.D.Clayton & S.A.Renvoize, Genera Graminum (1986), genus (463).
Native and naturalised. 6 species, from tropical regions. 2 species in Australia, NT and Qld. Also New Guinea and Malesia.
Habit. Perennial, decumbent (decumbent aquatics). Leaf blades broad or narrow, cordate or not cordate. Ligule an unfringed membrane.
Inflorescence. Inflorescence of spicate main branches or paniculate (spiciform or contracted, often with appressed branches), a spike-like panicle.
Spikelets. Spikelets subterete to dorsally compressed, 2 flowered, with 1 fertile floret, solitary. Fertile spikelets with lower incomplete floret(s), narrowly lanceolate, abaxial (with lower glume on side away from rachis), falling with glumes, with a distinctly elongated rachilla internode between glumes.
Glumes. Glumes unequal, (the upper) shorter than spikelet to about equal to spikelet (lower glume about half as long), shorter than adjacent lemmas to long relative to adjacent lemmas, awnless, similar (hyaline, not gibbous). Lower glume 1–3 nerved. Upper glume 3–7 nerved (usually acuminate).
Florets. Lower incomplete floret(s) sterile. Lemmas acute, acuminate or awnlike, more or less awned or awnless, 3–5 nerved, more or less equalling fertile lemmas to exceeding fertile lemmas, less firm than fertile lemmas to similar in texture to fertile lemmas (hyaline, lanceolate, acuminate), not becoming indurated. Fertile florets 1. Lemmas similar in texture to glumes to decidedly firmer than glumes (membranous to leathery), smooth, not becoming indurated, white in fruit, entire at apex, pointed, muticous, without a germination flap, 2 nerved or 3 nerved, glabrous, having flat margins not tucked into palea (except at the base). Palea relatively long, gaping, entire, textured like lemma. Lodicules 2. Stamens 3. Grain small, compressed dorsiventrally. Hilum short. Embryo large.
Kranz Anatomy. C3.
2n = 24.
Habitat. Hydrophytic to helophytic (in swamps).
Classification. Panicoideae; Paniceae.
Notes. A segregate from Panicum. There is also some resemblance to Sacciolepis, but the culms are filled with aerenchyma whereas those of Sacciolepis are hollow (Clayton & Renvoize, 1986).
Types Species. H. myuros (Lam.) P.Beauv.
Biogeographic Element. Clifford & Simon 1981, Simon & Jacobs 1990: IM -Trop. Am.