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Thuarea

Thuarea Syn. Pl. 1: 110 (1805).

Derivation:. Named for French botanist Aubert du Petit-Thoars, 1756–1831.

Key references (keys and floras):. G.Bentham, Flora Australiensis 7: 502–503 (1878); E.E.Henty, Manual Grasses New Guinea 188 (1969); M.Lazarides, Tropical Grasses S.E. Asia 145 (1980); J.C.Tothill and J.B.Hacker, Grasses of Southern Queensland 406–407 (1983); B.K.Simon, Key to Australian Grasses 169 (1993); D.Sharp and B.K.Simon, AusGrass (2002).

W.D.Clayton & S.A.Renvoize, Genera Graminum (1986), genus (490).

Native. 2 species, from Madagascar (1), Indomalaya (1), North Australia and New Guinea. 1 species in Australia, NT and Qld. Also New Guinea and Malesia.

Habit. Perennial, decumbent (creeping, mat-forming). Leaf blades broad or narrow. Ligule a fringe of hairs. Male and female-fertile spikelets segregated, in different parts of same inflorescence branch (the male spikelets distal to the female-fertile ones on the rachis).

Inflorescence. Inflorescence a peculiar spiciform `raceme', terminal, shortly peduncled, broad and winglike in the female-fertile part, narrow and beak-like in the upper male part, a spatheathe panicle, spatheate (the young inflorescence enclosed in the spathaceous blade of the uppermost culm leaf), racemes single, not in tight heads. Spikelet-bearing axes spikelike, with homomorphic spikelets, solitary.

Spikelets. Spikelets dorsally compressed, 2 flowered, with 1 fertile floret, discernably paired, discernably sessile and pedicelled (though the pedicels fused), in pedicelled/sessile combinations. Fertile spikelets with lower incomplete floret(s), elliptic or lanceolate or ovate, adaxial (with lower glume against rachis), not disarticulating (after anthesis the upper (male) spikelets fall, then the axis bends to enclose the developing fruit, and the flowering branch bends down to thrust the ripened seed into the sand).

Glumes. Glumes one per spikelet to two (the l.g. when present minute, hyaline), shorter than adjacent lemmas, the upper softly hairy, obtuse, awnless, non-keeled, dissimilar (when both present, the lower vestigial). Lower glume when present, 0 nerved. Upper glume 5 nerved.

Florets. Lower incomplete floret(s) male. Lemmas awnless, 5–7 nerved, more or less equalling fertile lemmas, less firm than fertile lemmas, not becoming indurated. Fertile florets 1. Lemmas decidedly firmer than glumes, smooth, papery, yellow in fruit, entire at apex, blunt, muticous, with a clear germination flap, 5–9 nerved, hairy (apically, otherwise glabrous), having flat margins not tucked into palea. Palea relatively long, entire, textured like lemma, 2 nerved. Lodicules 2. Stamens 3. Grain small to medium sized (3–4 mm long), compressed dorsiventrally. Hilum short. Embryo large, with one scutellum bundle. Pedicels discernible, but fused with rachis. Pedicelled spikelets with proximal incomplete florets or without proximal incomplete florets, 2 floreted (both or only one fertile).

Kranz Anatomy. C4.

Commonly adventive.

Habitat. Seashore sand. Species of open habitats.

Classification. Panicoideae; Paniceae.

Notes. Probably related to Brachiaria. The inflorescence is borne on a very short culm, and the capsules either become buried in the sand or float away in the sea (Clayton and Renvoize, 1986).

Types Species. T. involuta (G.Forst) Roem. & Schult.

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