8. DIARRHENEAE C.S. Campb.
Mary E. Barkworth

Plants perennial; rhizomatous. Culms annual, not branching above the base. Sheaths open, margins not fused; collars glabrous, without tufts of hair at the sides; auricles sometimes present; ligules stiff, scarious, ciliolate, those of the upper and lower cauline leaves usually similar; pseudopetioles absent; blades tapering both basally and apically, midveins usually eccentric, venation parallel, cross venation not evident; cross sections non-Kranz, without arm or fusoid cells; epidermes without microhairs or with unicellular microhairs, cells not papillate. Inflorescences terminal panicles. Spikelets laterally compressed, pedicellate, with (2)3–5(7) florets, distal floret(s) reduced and sterile, sometimes concealed by the subterminal florets; rachillas not prolonged beyond the terminal, sterile floret; disarticulation above the glumes and beneath the florets. Glumes 2, 1–5-veined, at least the upper glumes longer than 1/4 the length of the adjacent floret; florets laterally compressed; calluses glabrous or with a few hairs, rounded; lemmas lanceolate, cartilaginous to thinly coriaceous, 3(5)-veined, veins inconspicuous, apices unawned, sometimes mucronate; paleas from 1/2 as long as to subequal to the lemmas, 2-veined; lodicules 2, membranous, ciliate; anthers (1)2(3); styles 2, bases free. Caryopses obliquely ellipsoid, pericarp thick, easily peeled away at maturity, forming a conspicuous knob or beak, styles not persistent; hila linear; embryos 1/4–1/3 as long as the fruits. x = 10, 19.

There are 1–2 genera in the Diarrheneae. The tribe is sometimes placed in the Bambusoideae, sometimes in the Poöideae. Its inclusion in the Bambusoideae is supported by embryo characteristics and not strongly opposed by others, but it lacks some of the diagnostic features of that subfamily, e.g., fusoid cells, leaf blades with evident cross venation, and a complex midvein. Its inclusion in the Poöideae reflects the findings of the Grass Phylogeny Working Group (2001).

SELECTED REFERENCES Grass Phylogeny Working Group. 2000. A phylogeny of the grass family (Poaceae), as inferred from eight character sets. Pp. 3–7 in S.W.L. Jacobs and J. Everett (eds.). Grasses: Systematics and Evolution. CSIRO Publishing, Collingwood, Victoria, Australia. 408 pp.; Grass Phylogeny Working Group. 2001. Phylogeny and subfamilial classification of the grasses (Poaceae). Ann. Missouri Bot. Gard. 88:373–457; Koyama, T. and S. Kawano. 1964. Critical taxa of grasses with North American and eastern Asiatic distribution. Canad. J. Bot. 42:859–864; Tateoka, T. 1960. Cytology in grass systematics: A critical review. Nucleus (Calcutta) 3:81–110.