Common name
Tropical Beachgrass

Derivation
Thuarea Pers., Syn. Pl. 1: 110 (1805); after the French botanist Aubert du Petit Thouars.

involuta- from the Latin involvo (inroll). Leaf-blades inrolled.

Published in
Syst. Veg. 2: 808 (1817).

Habit
Perennial. Culms prostrate, 2.5–25 cm tall, rooting from lower nodes. Leaf-sheaths pilose. Ligule a fringe of hairs, 0.5–1 mm long. Collar pubescent. Leaf-blades lanceolate, 1.5–7 cm long, 3–10 mm wide. Leaf-blade surface pubescent. Leaf-blade margins scaberulous. Monoecious, with male and female spikelets in the same inflorescence.

Inflorescence
Inflorescence solid, a raceme, subtended by sheathless blades, enclosed. Peduncle terete (5mm long), widened at apex, disarticulating. Peduncle disarticulating above uppermost sheath. Peduncle base blunt. Racemes 1, erect, lanceolate, unilateral, 1–3 cm long, bearing few fertile spikelets, bearing 1(–2) fertile spikelets on each. Rhachis broadly winged, foliaceous, folded transversely to form a capsule, puberulous on surface, terminating in a sterile spikelet. Spikelet packing adaxial, regular, 1-rowed.

Spikelets
Spikelets solitary. Apical spikelets male (deciduous), 4–6 in number, 4 mm long. Fertile spikelets at least 3-flowered, comprising 1 fertile floret, without rhachilla extension, ovate, dorsally compressed, 4–5.4 mm long, falling entire, deciduous with accessory branch structures.

Glumes
Glumes one, the lower absent or obscure or one to two the lower present in some spikelets or two, thinner than fertile lemma. Lower glume (0–)1–2.5(–3.2) mm long. Upper glume ovate, 4–5.4 mm long, membranous, 5–7-nerved. Upper glume surface pubescent. Upper glume margins ciliate. Upper glume apex acute.

Florets
Basal sterile florets 1, with palea. Lemma of lower sterile floret similar to upper glume, ovate, 3–5.4 mm long, 90% of length of spikelet, membranous, 5–7-nerved, pubescent, ciliate on margins, acute. Palea of lower sterile floret pilose. Fertile lemma ovate, 4–5.4 mm long, indurate, of similar consistency on margins, 5-nerved. Lemma apex acute. Palea indurate. Anthers 3, 2.2–3 mm long. Male spikelets 2-flowered, 3.5–6 mm long. Male spikelet glumes 2, 3–5-nerved. Male spikelet lemma 8(–10)-nerved.

Continental Distribution:
Africa, Temperate Asia, Tropical Asia, Australasia, Pacific.

Australian Distribution:
Northern Territory, Queensland.

Northern Territory: Darwin & Gulf. Queensland: Cook, North Kennedy, South Kennedy, Port Curtis, Wide Bay.

Classification. (GPWG 2001):
Panicoideae: Paniceae

Notes
Native. A widespread species restricted to sandy coastal areas where it forms extensive stolons. Flowers Sept.–May.