| 1 | Leaves usually deciduous, with nerves ± curved, distinct, uniting or not but not forming an intramarginal vein. Seeds unilaterally winged. Inflorescence terminal and/or axillary. Petals with or without nectary scale, with punctate or linear glands. |
| 1' | Leaves evergreen, with nerves straight, obscure, uniting to form an intramarginal vein. Seeds winged all round. Inflorescence terminal. Petals with minute nectary scale and punctate glands. Sect. Isopterygium ENGL. |
| 2 | Petals without nectary scale, with linear glands. Inflorescence terminal and sometimes axillary. Staminodial fascicles (if well developed) recurved or cucullate. Leaves with nerves not arched or uniting. Sect. Cratoxylum. |
| 2' | Petals with nectary scale, with punctate glands. Inflorescence axillary on old or the base of young shoots. Staminodial fascicles (if well developed) never recurved. Leaves with nerves arched, uniting. Sect. Tridesmos (CHOISY) DYER. |
| 3 | Inflorescence paniculate, many-flowered, terminal and sometimes also axillary. Leaves very rarely glaucous beneath. Columella ¼ to nearlyi ½ as long as capsule. |
| 3' | Inflorescence of 1-5-flowered cymules, terminal and axillary or axillary only. Leaves nearly always glaucous beneath. Columella basal. |
| 4 | Capsule 4-6 mm ø. Seeds (7-) 12-17 per cell, obovoid-cylindric, 2-4 mm wide, with wing narrow at the base. Leaves 3½-14 cm long, oblong to elliptic or more rarely obovate. |
| 4' | Capsule 2-4(-5 ½) Ø. Seeds 4-6 per cell, cylindric to ovoid-cylindric, 1½-2 mm wide, with wing not narrowing at the base. Leaves 2-9 mm long, elliptic to obovate. |
| 5 | Seeds 10-13 per cell. Leaves acute to acuminate, 2-4 times as long as broad, obovate-oblong to obovate-oblanceolate or elliptic, not or scarcely papillose beneath, not yellow or orange beneath. |
| 5' | Seeds 4-7 per cell. Leaves rounded to obtuse-apiculate or rarely acute, usually 2 times as long as broad, elliptic, papillose-glaucous in the vein alveoli and usually yellow to orange beneath. |
