| 1 | Corolla pale yellow; flowers apparently solitary, axillary on an elongate, often unbranched inflorescence; style 2-2.5 mm long |
| 1' | Corolla blue, violet, purplish or whitish; style 3-12 mm long |
| 2 | Leaves conspicuously undulate-dentate; lobes about 1/4-1/2 total length of calyx |
| 2' | Leaves not conspicuously undulate-dentate; lobes reaching to near base of calyx |
| 3 | Low growing annuals (3-)8-30(-50) cm high; inflorescence dense, congested or glomerulate, conspicuously white-setose; corolla 3-6 mm diam.; style 3-3.5 mm long |
| 3' | Robust biennials or perennials 20-150(-200) cm high; inflorescence lax, paniculate; corolla 7-20 mm diam.; style 8-12 mm long |
| 4 | Calyx-lobes linear-acuminate; corolla rich blue or purplish; corolla-lobes 5-8 mm in diam.; leaves and stems green, rather densely, but not very pungently strigose-hispid |
| 4' | Calyx-lobes linear-oblong, obtuse or subacute; corolla pale blue or whitish-blue; corolla-lobes 3-6 mm in diam.; leaves and stems glaucous, rather thinly clothed with stout, pungent bristles |
