| 1 | Style-base sharply differentiated from and articulated with the nut proper (see E. spiralis). |
| 1' | Style-base confluent with the apex of the nut, not constricted at the base. Nut trigonous, usually reticulate under high magnification. Style 3-fid. Sp. 19 |
| 2 | Glumes indurated, cartilaginous on the back, with a distinct midnerve and finely many-nerved sides, not keeled or only obscurely so. Mostly coarse perennials with the stem as wide or almost as wide as the spikelet. Style 2-fid or 3-fid. Nut lenticular, stramineous or brown, 1½-2 mm long. Spp. 1-8. |
| 2' | Glumes membranous, with a distinct midnerve and nerveless sides, often keeled. Stem much narrower than the spikelet. |
| 3 | Style 3-fid. |
| 3' | Style 2-fid. Nut biconvex, smooth. |
| 4 | Nut triquetrous, trigonous, or lenticular, smooth or variously sculptured (finely reticulate, or cancellate i.e. with deep honeycomb reticulation), but not trabeculate, the epidermal cells inconspicuous, mostly shortly vertically oblong. |
| 4' | Nut obscurely trigonous or subterete, trabeculate (i.e. with some longitudinal ribs connected by numerous cross-ridges), the epidermal cells transversely linear or oblong. Lowest glume flower- bearing. Sp. 15 |
| 5 | Coarse or rather coarse perennials (excepts for small annual forms of E. congesta). Nut obtusely trigonous, not costate on the rounded angles, usually 1 mm or more long. Uppermost leaf-sheath distinctly mucronate at the mouth (muticous or almost so in E. congesta). |
| 5' | Dwarf, tufted annuals with capillary stems. Nut (in Mal. spp.) sharply triquetrous with costate angles, small, rarely up to 1 mm long. Uppermost leaf-sheath not mucronate. Spp. 13-14. 4. ser. Tenuissimae |
| 6 | Nut trigonous. Spp. 9-11 |
| 6' | Nut lenticular. Sp. 12 |
| 7 | Nut smooth or only finely reticulate under high magnification. Sp. 13. |
| 7' | Nut coarsely cancellate. Sp. 14. |
| 8 | Rather coarse, usually stoloniferous perennials. Style-base spongy. Nut more than 1 mm long, yellow or brown. Sp. 16 ser. Palustriformes |
| 8' | Small annuals, without stolons. Style-base not spongy. Nut less than 1 mm long, purplish or black. Spp. 17-18 ser. Maculosae |
