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| 1 Fresh plants strongly aromatic when bruised; corolla blue, 9-13 mm long; stem and leaves pubescent |
| 1 Fresh plants not aromatic when bruised; corolla predominantly white (in some species slightly pink or marked with yellow), 2-10 mm long; stem and leaves pubescent or glabrous. |
| ..2 Leaves glabrous; leaf margins crenate to serrate (sometimes entire in B. monnieri); flowers radially symmetrical. |
| ....3 Leaf blades typically with 5+ nerves; leaf margins crenate; stems pubescent; pedicels 10-12 mm long |
| ....3 Leaf blades with 1 nerve; leaf margins entire or serrate; stems glabrous; pedicels 5-30 mm long |
| ..2 Leaves pubescent (sometimes the pubescence fine or inconspicuous in B. innominata), leaf margins entire; flowers bilaterally symmetrical. |
| ......4 Corolla 4-10 mm long, white with a yellow throat; capsule ca. 5 mm long |
| ......4 Corolla 2-5 mm long, white or pink, without a yellow throat; capsule 2-3 mm long. |
| ........5 Leaves strongly clasping, mostly ovate; stamens 2 (or very rarely 4); [native] |
| ........5 Leaves only slightly clasping, mostly obovate; stamens 4; [a very rare introduction] |