| | 1. Some or all hairs stellate; anthers tapered, opening only by terminal pores; plant often prickly |
| |
| | 2. Stellate hairs scale-like, rays fused at center |
| S. elaeagnifolium |
| | 2' Stellate hairs not scale-like, rays free above stalk |
| |
| | 3. 1 anther > other 4; calyx tightly enclosing fruit |
| S. rostratum |
| | 3' Anthers ± equal; calyx not tightly enclosing fruit |
| |
| | 4. Leaf densely white-tomentose or velvety below |
| |
| | 5. Calyx not prickly; inflorescence branches 2–4; fruits several–many, 7–15 mm wide |
| S. lanceolatum |
| | 5' Calyx prickly; inflorescence branches 0; fruit 1, 35–50 mm wide |
| S. marginatum |
| | 4' Leaf sparsely tomentose below, not clearly white or velvety |
| |
| | 6. Leaf deeply pinnately lobed, lobes wavy to again lobed; annual; fruit red |
| S. sisymbriifolium |
| | 6' Leaf ± entire to wavy-lobed, teeth or lobes ± entire; perennial herb from rhizome; fruit yellow |
| |
| | 7. Corolla white or pale violet; stellate hairs fine, generally sessile; inflorescence generally raceme-like; fruit 8–20 mm |
| S. carolinense |
| | 7' Corolla generally purple; stellate hairs coarse, some stalked; inflorescence generally branched; fruit > 20 mm diam |
| S. dimidiatum |
| | 1' Hairs simple or branched, not stellate; anthers oblong, opening by terminal pores that become short slits; plant generally not prickly |
| |
| | 8. Leaf very deeply lobed |
| S. triflorum |
| | 8' Leaf entire to shallowly lobed (or deeply 2-lobed below middle) |
| |
| | 9. Corolla weakly lobed, lobes < tube + throat, generally spreading |
| |
| | 10. Shrub 2–4 m; leaf ± entire to deeply lobed; fruit orange-red |
| S. aviculare |
| | 10' Perennial or subshrub generally < 1 m; leaf ± entire to 1–2-lobed at base; fruit green to purplish |
| |
| | 11. Upper stem densely branched-hairy |
| S. umbelliferum |
| | 11' Upper stem glabrous or mostly simple-hairy |
| |
| | 12. Stem ± glabrous, clearly ridged; leaf sessile or gradually tapered to base |
| S. parishii |
| | 12' Stem generally soft- or glandular-hairy, smooth or weakly ridged; leaf base obtuse to subcordate |
| |
| | 13. Leaf generally 6–10 cm, oblong to ovate; fruit generally 15–25 mm; Channel Islands |
| S. wallacei |
| | 13' Leaf 2–7 cm, lanceolate to ovate; fruit 10–15 mm; mainland |
| S. xanti |
| | 9' Corolla lobes deep (= or > tube + throat), often reflexed |
| |
| | 14. Inflorescence axis generally forked, umbel-like clusters generally 2 |
| |
| | 15. Corolla violet to purple, each lobe with 2 shiny green spots at base; plant ± woody, ± climbing |
| S. dulcamara |
| | 15' Corolla white to pale violet, lobes not spotted; plant not woody, generally reclining |
| S. furcatum |
| | 14' Inflorescence umbel- or raceme-like, axis not forked |
| |
| | 16. Calyx enlarged and enclosing fruit base; fruit yellowish or green |
| S. sarrachoides |
| | 16' Calyx not enlarged, not enclosing fruit base; fruit black |
| |
| | 17. Anthers generally 2.5–4 mm |
| S. douglasii |
| |
| | 18. Seeds 1–1.5 mm; hairs ± appressed or curved, glands 0 |
| S. americanum |
| | 18' Seeds 1.5–2.5 mm; hairs ± spreading or curved, some glandular |
| S. nigrum
|