Common name
Spiny Burrgrass
Burr Grass

Derivation
Cenchrus L., Sp. Pl. 1049 (1753) & Gen. Pl. 5th edn, 470 (1754); from the Greek kenchros (millet, Panicum miliaceum).

incertus- from the Latin incertus (uncertain).

Published in
Boston J. Nat. Hist.1: 135 (1837).

Common synonyms
Cenchrus pauciflorus Benth.
Cenchrus tribuloides auct. non L.

Habit
Annual. Stolons absent. Culms erect or geniculately ascending, 5–80 cm tall. Ligule a fringe of hairs, 1–1.5 mm long. Leaf-blades 2–18 cm long, 2–6 mm wide. Leaf-blade margins scaberulous.

Inflorescence
Inflorescence solid, a spikelike panicle (bearing clusters of spikelets), linear, 2–8.5 cm long, 0.8–2 cm wide. Primary panicle branches accrescent to a central axis, with sessile scars on axis. Panicle axis angular, bearing deciduous spikelet clusters.

Spikelets
Spikelets subtended by an involucre. Involucre composed of bristles, connate into a cup below (cleft on 2 sides), with 2–7 mm connate, ovate or globose, 5.5–10.2 mm long. Involucre base obconical, glabrous or pubescent. Involucral bristles deciduous with the fertile spikelets, emerging irregularly from body of a burr, 8–40 in principal whorl, with longest bristle scarcely emergent, 2–5 mm long, flattened, rigid, retrorsely scaberulous, pubescent, spinose. Fertile spikelets 2-flowered, comprising 1 fertile floret, lower floret male, upper fertile, without rhachilla extension, ovate, dorsally compressed, acuminate, 3.5–5.8 mm long, falling entire, deciduous with accessory branch structures.

Glumes
Glumes thinner than fertile lemma. Lower glume ovate, 1–1.3 mm long, 33–50% of length of spikelet, membranous, 1-nerved. Lower glume lateral nerves absent. Lower glume apex obtuse or acute. Upper glume ovate, 2.8–5 mm long, 75–90% of length of spikelet, membranous, 5–7-nerved. Upper glume apex obtuse or acute.

Florets
Basal sterile florets 1, with palea. Lemma of lower sterile floret ovate, 100% of length of spikelet, membranous, 5–7-nerved, acute. Fertile lemma ovate, 3.4–5.8 mm long, coriaceous, much thinner on margins, 3-nerved. Lemma margins flat. Lemma apex acute. Palea coriaceous. Anthers 3, 0.5–2 mm long. Grain with adherent pericarp, ovoid, dorsally compressed, 1.3–3 mm long.

Continental Distribution:
Europe, Africa, Temperate Asia, Tropical Asia, Australasia, North America, South America.

Australian Distribution:
Western Australia, South Australia, Queensland, New South Wales, Victoria.

Western Australia: Drummond. South Australia: Eyre Peninsula, Murray, Northern Lofty. Queensland: Leichhardt, Darling Downs, Moreton, Maranoa. New South Wales: North Coast, Central Coast, South Coast, North-Western Slopes, Central-Western Slopes, North-Western Plains, South-Western Plains. Victoria: Riverina.

Classification. (GPWG 2001):
Panicoideae: Paniceae

Notes
Introduced. All mainland states except N.T. Flowers Dec.–May.

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