| 1 | Spikelets 20-25 mm long. Nut 3-3½ mm long |
| 1' | Spikelets and nuts much smaller, the former up to 12 mm long, the latter up to 2 mm. |
| 2 | Leaves reduced to mucronate or shortly laminate sheaths (i.e. leaf-blades very short in proportion to the size of the plant, more rarely a few of them elongated. Sheaths of leaves and bracts bearded at the mouth (more or less glabrescent with age). Glumes woolly-ciliate, at least when young. |
| 2' | Leaves with well-developed prominent blades. Sheaths not bearded at the mouth. Glumes glabrous. |
| 3 | Stems at least partly with 1-2 leaf-sheaths in or about the middle, very thin, ½-l(-1½)mm thick. Glumes dark brown, densely puncticulate (gland-dotted). Nut papillose on the angles at the top, otherwise smooth, brown, blackish blotched |
| 3' | No leaf-sheaths between the basal sheaths and the bracts. Stems generally thicker, (1½-)2-4 mm across. Glumes not puncticulate. Nut not papillose, concolorous. |
| 4 | Glumes blackish purple. Nut dull stramineous, more or less rugulose. |
| 4' | Glumes dark brown. Nut shining milky white, smooth |
| 5 | Inflorescence paniculate, compound or decompound, at least part of the primary branches with several to numerous spikelets. Spikelets ferrugineous to light brown. Nut setulose on the angles at the top. |
| 5' | Inflorescence racemose or almost so, or capitate; primary branches when present with 1-3 spikelets. Spikelets purplish, only in S. maschalinus often pale. Nut glabrous. |
| 6 | Nut scrobiculate by the wide, pitted epidermal cells, rufous, only slightly asymmetric. Bristles usually present. |
| 6' | Nut quite smooth (epidermal cells obscure, not pitted), milky white, distinctly asymmetric. Bristles absent. Spikelets 5-6 mm long |
| 7 | Leaves flat and 5-7 mm wide in the basal part, tapering into a very long subulate point. Spikelets 7-12 mm long, more or less falcate. Inflorescence stiffly erect |
| 7' | Leaves filiform almost from the base. Spikelets 5-6 mm long, not or hardly falcate. Inflorescence more or less drooping |
| 8 | Hypogynous bristles absent. Spikelets 9-11 mm long |
| 8' | Hypogynous bristles present. Spikelets up to 8 mm long, often much shorter. |
| 9 | Hypogynous bristles plumose in the lower part. Rhizome creeping; stems distant or somewhat tufted. Inflorescence capitate |
| 9' | Hypogynous bristles scabrous, not plumose. Rhizome cespitose, stems densely tufted. Inflorescence racemose, in S. setiformis strongly contracted and head-like. |
| 10 | Inflorescence dense, almost capitate (occasionally with a fascicle of 1-3 spikelets lower down). Nut smooth, brown |
| 10' | Inflorescence loose, racemose. Nut slightly scrobiculate, whitish. |
| 11 | Spikelets 6-8 mm long, purple. Anthers 2-3 mm. Nut 1½-2 mm long, Stems erect, rigid, 10-40 cm tall |
| 11' | Spikelets 2-4 mm long, pale or purplish variegated. Anthers c. 1½ mm. Nut 1-1⅓ mm long. Stems often decumbent and rooting at the nodes, 4-20 cm long, rarely longer. |
