| 1 | Rachilla of the spikelets persistent. Glumes acropetally deciduous. |
| 1' | Rachilla deciduous, spikelets falling off entire. Glumes distichous. Cauline leaves reduced to bladeless sheaths. Inflorescence capitate. Sp. 11 |
| 2 | Nut obovate, oblong-obovate, orbicular, pyriform, or turbinate. |
| 2' | Nut subcylindric, with almost parallel edges. |
| 3 | Stigmas 3; style triquetrous, usually glabrous. Nut trigonous or triquetrous (see F. globulosa, F. scaberrima, and F. cymosal). |
| 3' | Stigmas 2; style flat, usually ciliate. Nut biconvex or planoconvex. Glumes spirally arranged. |
| 4 | Glumes spirally arranged. |
| 4' | Glumes distichously arranged (see F. eragrostis!). |
| 5 | Nut smooth or verruculose. |
| 5' | Nut coarsely tuberculate, pyriform. Cauline leaves reduced to bladeless sheaths. Inflorescence anthelate. Sp. 31. |
| 6 | Inflorescence anthelate or capitate. |
| 6' | Inflorescence consisting of a single spikelet. Spp. 29-30. |
| 7 | Ligule a fringe of short hairs. Spp. 1-6 |
| 7' | Ligule.absent. |
| 8 | Cauline leaves reduced to bladeless sheaths. Spp. 7-13 |
| 8' | Cauline leaves with well developed blades. |
| 9 | Glumes not or only microscopically ciliolate. |
| 9' | Glumes long-ciliate. Spp. 23-28. |
| 10 | Rather stout perennials. Spp. 14-20. |
| 10' | Small annuals. Spp. 21-22. |
| 11 | Nut large, 2-3 mm long, usually coarsely tuberculate. Inflorescence usually consisting of a single spikelet. Sp. 32. |
| 11' | Nut much smaller, smooth or verruculose. Inflorescence with a few to numerous spikelets. Spp. 33-44. |
| 12 | Nut not coarsely rugulose. |
| 12' | Nut coarsely rugulose by transverse ridges. Cauline leaves reduced to bladeless sheaths. Inflorescence consisting of a single spikelet. Spp. 72-74 |
| 13 | Glumes ovate or orbicular, less than twice as long as broad. Inflorescence usually anthelate. |
| 13' | Glumes oblong-ovate or oblong-lanceolate, twice or more than twice as long as broad. Inflorescence usually consisting of a single spikelet. Spp. 68-71 |
| 14 | Ligule a fringe of short hairs, very rarely membranous. |
| 14' | Ligule absent. |
| 15 | Nut smooth. Spp. 45-50 |
| 15' | Nut trabeculate. Spp. 51-58 |
| 16 | Spikelets terete or subterete, 2-4 mm wide. Spp. 59-62 |
| 16' | Spikelets angular, 1-1½ mm wide. Spp. 63-67 |
| 17 | Inflorescence consisting of a single spikelet. Cauline leaves reduced to bladeless sheaths. Nut without clavate appendages. Sp. 75 |
| 17' | Inflorescence anthelate. Cauline leaves with well developed blades. Nut ornamented with rows of clavate appendages. Sp. 76 |
