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Acrachne

Acrachne Wright & Arn. ex Chiov., Annu. Ist. Bot. Roma 8: 361 (1907).

Derivation:. From Latin acris (sharp or pointed) and Greek achne (glume), alluding to the pointed glumes and lemmas.

Key references (keys and floras):. C.A.Gardner, Flora of Western Australia 1 Gramineae 208–209 (1952); M.Lazarides, Tropical Grasses S.E.Asia 166–167 (1980); J.C.Tothill and J.B.Hacker, Grasses of Southern Queensland 78–79 (1983); M.Lazarides, F.Quinn and J.Palmer, Flora of the Kimberley Region 1120 (1992); B.K.Simon, Key to Australian Grasses  61 (1993); D.Sharp and B.K.Simon, AusGrass (2002); K.Mallet (ed.), Flora of Australia 44B: Poaceae 3: 313–314 (2005).

W.D.Clayton & S.A.Renvoize, Genera Graminum (1986), genus (371).

Native. 3 species, from Ethiopia, southern Africa, Indomalayan region, Australia. 1 species in Australia, WA, NT, and Qld. Also Malesia.

Habit. Annual, tufted. Leaf blades broad to narrow. Ligule a fringed membrane to a fringe of hairs.

Inflorescence. Inflorescence of spicate main branches, of digitate or subdigitate racemes or spikes, subdigitate (usually with the lower spikes scattered, but becoming subdigitate above) or non-digitate (A. racemosa).

Spikelets. Spikelets laterally compressed, more than 2 flowered, with 2 or more fertile florets, solitary, subsessile; with rachilla terminating in a floret. Fertile spikelets adaxial (with lower glume against rachis), disarticulating above glumes or falling with glumes or not disarticulating (the spikelet often falling wholly or in part before all the lemmas have been shed).

Glumes. Glumes relatively large, more or less equal, shorter than spikelet, shorter than adjacent lemmas, awnless (but subulate via an excurrent mid-nerve), keeled, similar (thinly cartilaginous). Lower glume 1 nerved. Upper glume 1 nerved.

Florets. Fertile florets 8–20. Lemmas similar in texture to glumes to decidedly firmer than glumes (cartilaginous), not becoming indurated, incised, mucronate (from the midnerve), 3 nerved (the laterals closer to the margins than to the mid-nerve, and excurrent as small teeth), glabrous, 1 keeled. Palea 2 nerved. Lodicules 2. Stamens 3.  Grain small, ellipsoid, deeply longitudinally grooved (on the hilar side), compressed dorsiventrally, sculptured. Hilum short. Embryo large.

Habitat. Mesophytic. Sandy savanna. Shade species and species of open habitats.

Classification. Chloridoideae; Cynodonteae.

Notes. The ligule is noteworthy in that, although membranous, it is derived from the ciliate type found in Eragrostis. The outer surface is pilose, so that the whole structure appears to be composed of a fringe of hairs which have partially fused together to form a membrane (Phillips, Flora of Tropical East Africa Gramineae 2: 260 (1974)).

Types Species. A. verticillata (Roxb.) Chiov. = A. racemosa (B. Heyne ex Roem. & Schult.)Ohwi.

Biogeographic Element. Clifford & Simon 1981, Simon & Jacobs 1990: Old World Tropics.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith