| 1 | Stems transversely septate, i.e. with a single large central cavity divided into several chambers by distinct transverse septa visible (at least when dry) from the outside. |
| 1' | Stems not transversely septate. |
| 2 | Stems tufted on a short rhizome with elongated stolons sometimes bearing subglobose tubers. Spikelets 3-6 mm wide. Glumes greyish, 4-6½ mm long. Bristles 6-8. Nut 1½-1 mm long. |
| 2' | Stems in a close linear series on a very stout, shortly creeping rhizome never producing tubers. Spikelets 8-9 mm wide. Glumes light brown, 7½-9 mm long. Bristles 8-10. Nut 21/5-2½ mm long. |
| 3 | Glumes cartilaginous, not or hardly keeled, finely many-nerved, usually with prominent midnerve. Nut lenticular, stramineous to brown, 1½-2½ mm long. Style 2-fid or 3-fid. Spikelets hardly (if at all) wider than the stem (E. ochrostachys often excepted). |
| 3' | Glumes thinly membranous, often keeled, with distinct midnerve but nerveless sides. Nut triquetrous, trigonous, or lenticular. Spikelet much wider than the stem. |
| 4 | Nut constricted below the apex into a short but definite neck, the apex expanded. Stems acutangular. |
| 4' | Nut not constricted below the apex, without neck. |
| 5 | Epidermal cells of the nut for the greater part transversely oblong to linear, shallowly pitted. Glumes appressed, not in 4 rows. Spikelet terete. Stems triquetrous, usually 3-4 mm wide. |
| 5' | Epidermal cells of the nut for the greater part isodiametric, hexagonal, deeply pitted. Glumes finally subsquarrose, almost in 4 rows. Spikelet angular. Stems acutely 4-5-angled, c. 2 mm wide. |
| 6 | Glumes very obtuse to truncate, very densely imbricate (the exposed part broader than long, only ½-1 mm long). |
| 6' | Glumes obtuse, not particularly densely imbricate (the exposed part longer than broad, 2-3 mm long). |
| 7 | Stems triquetrous at least in the upper part. Style-base c. ⅓ as long and ½ as wide as the nut. Epidermal cells of the nut transversely oblong-linear to linear, in c. 20 vertical series on either face |
| 7' | Stems terete. Style-base c. ¾ as long and almost as wide as the nut. Epidermal cells of the nut transversely oblong, in c. 30 vertical series on either face |
| 8 | Epidermal cells of the nut small, not inflated, transversely oblong, in 15-20 vertical rows on either face. Nut with prominent longitudinal ridges |
| 8' | Epidermal cells of the nut large, strongly inflated, isodiametric or slightly transversely elongated, in c. 12(-15) vertical rows on either face. Nut not longitudinally ridged. |
| 9 | Style 3-fid. |
| 9' | Style 2-fid. Nut lenticular. |
| 10 | Nut lenticular, plano-convex or biconvex. Uppermost leaf-sheath prominently mucronate. |
| 10' | Nut trigonous, subterete or triquetrous. |
| 11 | Nut trabeculate (with some longitudinal ribs connected by numerous cross-ridges) or cancellate (with deep, regular honey-comb reticulation). Stems capillary. |
| 11' | Nut smooth, neither trabeculate nor cancellate, only finely reticulate under high magnification. |
| 12 | Nut obovoid, sharply triquetrous, almost truncate at the apex, cancellate. Style-base about as wide as the nut, 3-lobed, the lobes decurrent on the angles of the nut. |
| 12' | Nut obovoid-oblong, obscurely trigonous or subterete, trabeculate. Style-base minute, at most ½ as wide as the nut, not decurrent. |
| 13 | Style-base not constricted at the base, confluent with the apex of the nut and seemingly a continuation of it, but of different colour and texture. Dwarfish (stems 1-7 cm by ¼-⅓ mm), often with filiform stolons ending in small fusiform tubers. |
| 13' | Style-base constricted at the base, sharply differentiated from and articulated with the nut. |
| 14 | Nut triquetrous with costulate angles, very small (c. ½ mm long). Bristles absent (in Malesian specimens) |
| 14' | Nut trigonous, not costulate, 4/5-1½ mm long. Bristles 6, as long as or longer than the nut. |
| 15 | Stems acutely quadrangular. Bristles densely scabrous to barbellate- subplumose. Nut 1¼-1½ mm long, crowned by a large, cap-like style-base. |
| 15' | Stems terete, more or less angular-ribbed but not quadrangular. Bristles more or less scabrous, not subplumose. Nut 4/5-1.2 mm long with short- pyramidal style-base. |
| 16 | Style-base 3/5 to almost as wide as the nut. Glumes 2-2½(-3) mm long. Uppermost leaf-sheath truncate or slightly oblique, distinctly mucronate. Nut 1-1.2 mm long |
| 16' | Style-base ⅓-½ as wide as the nut. Glumes 1½-2 mm long. Uppermost leaf-sheath usually oblique, not or but minutely mucronate. Nut 4/5-1 mm long. |
| 17 | Rather coarse, stoloniferous perennial. Nut 1½-1⅔ mm long, yellowish or pale brown. Glumes c. 4½ mm long |
| 17' | Small annuals without stolons. Nut less than 1 mm long, blackish when ripe. Glumes at most 2 mm long. |
| 18 | Spikelets c. 3 mm thick. Glumes scarcely keeled, 1¾-2 mm long. Bristles 6-8, slightly longer than the nut, ferrugineous to brown. Nut ¾-9/10 mm long. |
| 18' | Spikelets 1½-2 mm thick. Glumes keeled, up to 1⅓ mm long. Bristles 3-4(-6), shorter than to as long as the nut, whitish, translucent, sometimes absent. Nut ½-⅔ mm long. |
