Key to species in the genus Biancaea

1a. Leaves opposite ........................................................................................................................................................... B. oppositifolia

1b. Leaves alternate..................................................................................................................................................................................2

2a. Pedicels longer than 1 cm ...................................................................................................................................................................3

2b. Pedicels 0.8 cm long or less ...............................................................................................................................................................4

3a. Pedicels 3–4 cm long...................................................................................................................................................... B. decapetala

3b. Pedicels less than 2 cm long...............................................................................................................................................................5

4a. Pinnae pairs per leaf 2–6 pairs, leaflet pairs per pinna (3–)5–9 pairs ................................................................................................6

4b. Pinnae pairs per leaf 7–10(–14) pairs, leaflet pairs per pinna 9–18 pairs ....................................................................... B. parviflora

5a. Pedicels to 1.5 cm, leaflet apex rounded or obtuse ............................................................................................................. B. millettii

5b. Pedicels 1.5–2 cm, leaflet apex emarginate or retuse........................................................................................................... B. sappan

6a. Leaflets opposite, ovate to elliptic, apex acute to obtuse but rounded at the very tip; sepals scabrid on the outer surface, inner surface sparsely so............................................................................................................................................................. B. scabrida

6b. Leaflets alternate to subopposite, oblong-elliptic, apex rounded, sepals densely pubescent on both surface ............ B. godefroyana