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| 1 Corollas 4-11 cm long, the limb with 5 shallow sinuses alternating with acuminate lobes; fruits erect; [section Datura]. |
| ..2 Leaf blades elliptic to narrowly ovate, margins pinnately lobed |
| ..2 Leaf blades broadly ovate, margins sinuate-dentate. |
| ....3 Corollas < 6 cm long; leaf blade < 1.5 × as long as wide; spines of fruit unequal along axis of fruit, some > 1.5 cm long |
| ....3 Corollas 6-9 cm long; leaf blade > 1.5 × as long as wide; spines of fruit +/- equal along axis of fruit, all < 1.5 cm long |
| 1 Corollas usually greater than 10 cm long, limb with 5 lobules alternating with acuminate lobes; fruits pendent; [section Dutra]. |
| ......4 Plants perennial, often with woody base; leaves and stems glabrescent; corollas white, purple, or yellow, with single, double, or triple whorls; fruits spineless, pericarp tuberculate |
| ......4 Plants perennial, with herbaceous base; leaves and stems pubescent; corollas white (sometime purple-tinged), with a single whorl; fruits with spines, pericarp pubescent. |
| ........5 Corolla limbs with 5 acuminate lobes +/- equal to 5 lobules; calyces villous-pubescent (especially along veins); abaxial leaf surface villous-pubescent (especially along veins), trichomes spreading |
| ........5 Corolla limbs with 5 acuminate lobes longer than the 5 lobules; calyces canescent-puberulent (especially along veins); abaxial leaf surface canescent-puberulent (especially along veins), trichomes short-appressed or curved |