Uranthoecium Hooker's Icon. Pl. Tab. 3073 (1916).
Derivation:. From Greek ouranos (vaulted roof) and thekion (little box), referring to the particular shape of the caryopsis.
Key references (keys and floras):. J.W.Vickery, Flora of New South Wales, Gramineae 19: 263–264 (1975); M.Lazarides, Flora of Central Australia 483 (1981); J.C.Tothill and J.B.Hacker, Grasses of Southern Queensland 424–425 (1983); J.P.Jessop, Flora of South Australia 4: 1980 (1986); B.K.Simon, Key to Australian Grasses 174 (1993); D.Sharp and B.K.Simon, AusGrass (2002); J.P.Jessop, Grasses of South Australia 490 (2006); S.W.L.Jacobs, R.D.B.Whalley & D.J.B.Wheeler, Grasses of New South Wales, 4th ed, 392 (2008).
W.D.Clayton & S.A.Renvoize, Genera Graminum (1986), genus (513).
Native, endemic. 1 species, from arid mainland Australia. NT, SA, Qld, and NSW.
Habit. Annual (or short-lived perennial), tufted. Leaf blades narrow. Ligule a fringed membrane to a fringe of hairs.
Inflorescence. Inflorescence of spicate main branches (of short spikes, each of 2–4 spikelets, the spikes on a common, flattened cartilaginous axis), a spike-like panicle, contracted. Spikelet-bearing axes falling entire (the short spikes falling with the adjacent internode of the fragile common axis).
Spikelets. Spikelets dorsally compressed, 2 flowered, with 1 fertile floret, solitary, sessile. Fertile spikelets with lower incomplete floret(s), lanceolate, falling with glumes (and with the spike).
Glumes. Glumes relatively large, unequal, shorter than adjacent lemmas (the upper 1/2, the lower 1/4 its length), hairless, glabrous, awnless, similar (firmly chartaceous, truncate). Lower glume 6–7 nerved. Upper glume distinctly saccate (gibbous), 7 nerved.
Florets. Lower incomplete floret(s) sterile. Lemmas membranous along the midline, leathery on the sides, caudate-acuminate, awnless (but caudate-acuminate), 5–7 nerved, not becoming indurated (but cartilaginous between the outer nerves). Fertile florets 1. Lemmas ovate-elliptic, subulate-caudate above, decidedly firmer than glumes, smooth, becoming indurated (thinly), yellow in fruit, entire at apex, pointed, awned, 5 nerved, glabrous, having flat margins not tucked into palea. Awns 1, apical, non-geniculate. Palea entire (apically prolonged, the tip caudate), with apical setae, textured like lemma, indurated, 2 nerved. Lodicules 2. Stamens 3. Grain small. Hilum short. Embryo large.
Kranz Anatomy. C4.
Habitat. Xerophytic. Grassland on clay. Species of open habitats.
Classification. Panicoideae; Paniceae.
Notes. A monotypic genus restricted to arid regions of central Australia. This taxon was originally described in Rottboellia, evidently on the basis of the mode of disarticulation; however the spikelet characteristics are definitely panicoid. The biserrate main axis, the disarticulation at the rachis joints and branches ending in a naked point are important characters that Uranthoecium has in common with Stenotaphrum (Webster, 1987).
Types Species. U. truncatum (Maiden & Betche) Stapf.
Biogeographic Element. Clifford & Simon 1981, Simon & Jacobs 1990: Endemic.