| | 1. Nectary pits 2 per corolla lobe (sometimes appearing as 1 due to overlapping fringes) |
| |
| | 2. Stem generally < 1 m, < 1 cm wide; cauline leaves opposite or some alternate; corolla generally bluish, 4- or 5-lobed |
| S. perennis |
| | 2' Stem generally > 1 m, > 1.5 cm wide; cauline leaves whorled; corolla yellowish green, 4-lobed |
| S. radiata |
| | 1' Nectary pit 1 per corolla lobe |
| |
| | 3. Leaves at low to mid stem widely elliptic, not white-margined — inflorescence dense, < 0.5 dm wide |
| S. fastigiata |
| | 3' Leaves at low to mid stem narrower than widely elliptic, white-margined (sometimes narrowly so) |
| |
| | 4. Inflorescence ± open, generally > 1 dm wide or lowest branches < 1 dm from stem base and widely divergent, or both |
| |
| | 5. Cauline leaves whorled, uppermost sometimes opposite |
| S. albomarginata |
| | 5' Cauline leaves opposite |
| |
| | 6. Stems, lower leaf surfaces glabrous; basal, lower cauline leaves generally > 1 cm wide; nectary pits U-shaped |
| S. parryi |
| | 6' Stems, lower leaf surfaces puberulent; basal, lower cauline leaves generally < 1 cm wide; nectary pits oblong-obovate |
| S. puberulenta |
| | 4' Inflorescence dense, sometimes interrupted, < 1 dm wide, lowest branches > 1 dm from stem base, short, strongly ascending — upper pedicels generally arising directly from main stem |
| |
| | 7. Nectary-pit margin with 2 oblong, fringed lobes |
| S. tubulosa |
| | 7' Nectary-pit margin fringed but not lobed |
| |
| | 8. Nectary pits round to ± square; stamen bases with a low, fringed ridge between |
| S. neglecta |
| | 8' Nectary pits oblong; stamen bases with ± 2 mm scales between |
| S. albicaulis |
| | 9. Stems, leaf lower surfaces puberulent; larger leaves rounded at tip |
| var. albicaulis |
| | 9' Stems, leaves glabrous; larger leaves generally acute |
| var. nitida
|