| | 1. Perennial from long rhizomes; fruit ± compressed, 3–4-angled, 2-ribbed between angles |
| S. arvensis |
| | 1' Annual from taproots; fruit weakly to strongly flattened |
| |
| | 2. Stems slender; leaves deeply lobed, lobes toothed and often with smaller secondary lobes; fruit only slightly flattened, transversely roughened; ligule > corolla tube; uncommon |
| S. tenerrimus |
| | 2' Stems stout; leaves toothed or with wide lobes; fruit flat, with thin edges, smooth or cross-roughened; ligule < or = corolla tube; widespread and common |
| |
| | 3. Basal lobes of leaves rounded; fruit 3-ribbed on each side, otherwise smooth; ligule < corolla tube |
| S. asper subsp. asper |
| | 3' Basal lobes of leaves acute; fruit 2–4-ribbed and cross-wrinkled; ligule ± = corolla tube |
| S. oleraceus
|