POACEAE Tribe ARUNDINELLEAE
Annual or perennial herbs. Leaf-blades linear or sometimes linear-lanceolate, usually flat; ligule very short, membranous to ciliate. Inflorescence a panicle, often large, the spikelets often associated in clusters of 3. Spikelets lanceolate, all alike, 2-flowered, the lower floret male or barren, the upper bisexual with an obtuse to pungent callus at the base, the rhachilla disarticulating between the florets or beneath each floret; glumes persistent, usually unequal the upper exceeding the florets, membranous to coriaceous, often brown and beset with tubercle-based hairs; lower lemma similar to the glumes, 3-7-nerved, accompanied by a narrow palea; upper lemma ± terete, smaller than the lower, firm in texture, 5-11-nerved, sometimes decorated with tufts of hair, 2-toothed at the tip, the teeth sometimes produced into bristles, awned from the sinus; awn geniculate with a twisted column, usually deciduous above the base and usually flattened in cross-section; palea-keels often winged; lodicules 2, cuneate; stamens 2-3; stigmas 2. Grain with large embryo and linear or punctiform hilum; starch grains compound. Chromosomes small, basic number mostly 10 or 12.
Genera ± 9; tropics, often favouring infertile soils; 2 genera in Pakistan, each with a single species.
The tribe is allied to Paniceae, as is suggested by the sexual dimorphism of the two florets, as well as by the leaf-anatomy. However, there are anatomical features which also suggest a relationship with Arundineae. The tribe can usually be recognised readily enough by the lanceolate spikelets with their papery brown glumes often beset with tubercle-based hairs.
Inter-relationships among the species of Arundinelleae are extremely complicated, and there are few clear disjunctions between them. As a result there is much disagreement over generic limits, some authors favouring few genera of broadly recognisable facies, others preferring small closely defined genera which are necessarily much more numerous.
The callus of the upper floret is an important character. If the awn of a mature spikelet is gently pulled, the floret may be drawn out and the callus at its base examined. The spikelets complete their growth after the panicle has been exserted from the uppermost sheath, and juvenile specimens with undeveloped awns often puzzle the unwary.