| 1 | Anthers not versatile, not sagittate (thecae connate at the base). Leaves reticulately veined. Ser. Adnatae. |
| 1' | Anthers versatile, sagittate (thecae separate at the base). Veins reticulate-scalariform (also reticulate in B. arborescens). Ser. Sagittatae. |
| 2 | Leaves 8-25 by 3-8 cm; apex acuminate, rarely short-acuminate. Pedicels articulated |
| 2' | Leaves 3½-1½ by 2¼-4¾ cm; apex obtuse, sometimes emarginate. Pedicels not articulated |
| 3 | Filaments bicoloured, contracted and whitish at the apical part (c. 1/5 of the length). |
| 3' | Filaments concolorous, gradually narrowed towards the apex and not whitish at the apical part. |
| 4 | Flowers ¾-4 mm pedicelled. |
| 4' | Flowers sessile, articulated at the base. Leaf apex usually obtuse or rounded, rarely apiculate, acute, acuminate or emarginate, (12-)26-80 by (4½-)6½-l6 cm; veins reticulate-scalariform. |
| 5 | Leaf apex short-acuminate or acuminate; blade 9-40 by 3-12½ cm, veins reticulate-scalariform. Pedicels articulated, ¾-2 mm |
| 5' | Leaf apex usually obtuse or rounded, rarely apiculate, acute, acuminate, or emarginate; blade 472-26(-35) by 1¾-7(-9) cm; veins reticulate or reticulate-scalariform. Pedicels usually not articulated, (l-)2-4 mm |
| 6 | Petiole usually 0 or very short (c. ½ cm) |
| 6' | Petiole distinct, (1½-)3-6 cm |
| 7 | Filaments smooth. Leaves oblanceolate to narrowly oblanceolate, (16-)30-80 by (5-)6½-16 cm; petiole distinct, 2-3(-6) cm |
| 7' | Filaménts papillose. Leaves smaller, obovate-oblong, oblanceolate or spathulate, 7½-31 by 4-10½ cm; petiole usually 0, sometimes up to 1½(-3) cm |
