| | 1. Annual; inflorescence 1–5 cm, terminal and axillary at ± most stem nodes; lemma leathery, tip beaked |
| S. vaginiflorus |
| | 1' Perennial; inflorescence 8–80 cm, generally terminal, sometimes axillary at some stem nodes; lemma membranous, tip obtuse to acute |
| |
| | 2. Inflorescence ± spike-like, cylindric, dense; 1° branches, generally < 3 cm, appressed, obscure |
| |
| | 3. Upper glume length > 0.5 × lemma, lanceolate, tip entire; glume and lemma midveins ± scabrous at 20× |
| S. contractus |
| | 3' Upper glume length < 0.5 × lemma, ovate, tip generally irregularly toothed; glumes and lemma midveins ± glabrous at 20× |
| S. indicus |
| | 2' Inflorescence oblong to triangular in outline, ± open, sometimes enclosed by sheath; 1° branches generally > 3 cm, generally spreading |
| |
| | 4. Anthers 1–1.8 mm; glume and lemma backs ± rounded, midvein ± glabrous at 20×; lowest inflorescence branches generally > 6 cm; old sheath bases straw-colored, glossy |
| S. airoides |
| | 4' Anthers < 1 mm; glume and lemma backs ± keeled, midvein ± scabrous at 20×; lowest inflorescence branches generally < 6 cm; old sheath bases brown, dull |
| |
| | 5. 1° inflorescence branches ± spike-like; 2°, 3° branches ± appressed, ± obscure |
| S. cryptandrus 5' 1° inflorescence branches ± raceme-like; 2°, 3° branches spreading, evident.....-> S. flexuosus
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