| | 1. Annual; central flower of a node generally higher than lateral flowers |
| |
| | 2. Plant ± slender; stem branched above middle; spike 4–6 mm wide |
| S. bigelovii |
| | 2' Plant generally rounded or ovoid; stem branched throughout; spike 2–4 mm wide |
| S. europaea |
| | 1' Perennial from rhizomes; flowers of a node generally at same level |
| |
| | 3. Spike 2–3 mm wide, distal internodes lacking flowers |
| S. subterminalis |
| | 3' Spike 3–5 mm wide, flowered to tip |
| |
| | 4. Stem axis generally erect, branches generally ascending; ne Mojave Desert |
| S. utahensis |
| | 4' Stem axis generally creeping, rooting at nodes, branches decumbent to erect; coastal, s San Joaquin Valley |
| S. virginica
|