| 1 | Spikelets 2-flowered. Filaments hardly lengthening after anthesis, those of the two flowers cohering with their tips. |
| 1' | Spikelets 1-flowered. Filaments strongly lengthening after anthesis, their tips included by the apex of the longest empty glume(s). |
| 2 | Endocarp transversely grooved on the inner side (the 4-6 annular grooves to be observed in a longitudinal section of the fruit) |
| 2' | Endocarp smooth on the inner side, not grooved |
| 3 | All the filaments of one flower included by the involute apex of the uppermost sterile glume. Inflorescence more or less effuse, paniculate, rather flaccid, the primary branches usually several to many in each fascicle. Nut narrow, oblong, (2-)3½-5 by 1-1½ mm |
| 3' | The filaments of one flower included by the apices of 2-3 upper sterile glumes. Inflorescence narrow, spike-like, stiff and prickly, the primary branches 1-3 in each fascicle. Nut broader, globose, ovoid, or ellipsoid, 4-6 by 1¾-4mm. |
| 4 | Filaments with ciliolate-scabrid margins; anthers 1½-2 mm long; appendage of the connective short (¼ mm). Nut globose or ovoid, not or scarcely angular, distinctly mucronate, 3-4 mm wide. |
| 4' | Filaments glabrous; anthers 3-4 mm long, with subulate, ½-¾ mm long appendage of the connective. Nut ellipsoid, trigonous, not or scarcely mucronate, 1¾-2(-2½) mm wide. |
