| 1 | Stamens 8, in 2 whorls of 4. Inflorescence branches 4-angular (at least when young). Calyx subtruncate with minute, acute teeth. Bracts caducous. Pedicels of lateral flowers of terminal cymes over 5 mm, slender. Septum of endocarp swollen to at least V3 of the diameter of the fruit. Branchlets subterete. Domatia occasional, suborbicular. SUBG. MANGLESIA |
| 1' | Stamens 4-5(-6), in one whorl. Inflorescence branches terete. Calyx distinctly lobed. Bracts subpersistent. Septum of endocarp wedge-shaped. SUBG. MASTIXIA. |
| 2 | Inflorescence branches of the first order (sub)opposite or decussate. Branchlets and leaves generally (sub)opposite or decussate; nodes flattened. Fruits generally ovoid. Ser. Oppositae. |
| 2' | Inflorescence branches of the first order scattered. Branchlets and leaves scattered; nodes terete. Fruit generally ellipsoid or oblong. Ser. Alternae. |
| 3 | Flowers basically 5-merous. |
| 3' | Flowers basically 4-merous. |
| 4 | Sepals less than half as long as wide. Inflorescence subglabrous to puberulous. Fruit ovoid to oblong, with inconspicuous persistent sepals |
| 4' | Sepals almost as long as wide. Inflorescence velutinous to woolly. Fruit elongate-ovoid, with conspicuous persistent sepals |
| 5 | Sepals almost as long as wide. Inflorescence puberulous to woolly. Corolla puberulous to villous outside. Leaves acute or shortly acuminate, 5-24 by 2-12 cm. Fruit with conspicuous persistent sepals |
| 5' | Sepals less than half as long as wide. Inflorescence (sub)glabrous. Corolla glabrous outside. Leaves abruptly caudate to cuspidate, 4-12 by 2-5½ cm- Fruit with obscure calyx teeth. |
| 6 | Leaves strictly opposite; petioles stout. Leaves thick-coriaceous; nervation prominent, with intermediary nerves. Inflorescence stout with lower bracts up to 5 mm. Fruit 1½ cm ø |
| 6' | Leaves (sub)opposite or alternate; petioles slender. Leaves chartaceous to subcoriaceous; nervation rather weak, without intermediary nerves. Inflorescence slender with bracts all under 3 mm. Fruit up to 1 cm ø |
| 7 | Branchlets woolly. Leaves 13-30 by 5½-15 cm, with midrib and nerves (even veinlets) woolly to villous; petioles stout, 4 cm or longer, woolly. Fruit over 4 by 2 cm. Flowers 5-merous |
| 7' | Branchlets not woolly. Petioles up to 4 cm. Fruit up to 4 cm long. |
| 8 | Flowers basically 4-merous. |
| 8' | Flowers basically 5-merous. |
| 9 | Leaves glaucous and waxy below, thick-coriaceous, with intermediary nerves; apex apiculate. Sepals as long as wide |
| 9' | Leaves not glaucous and waxy below, without intermediary nerves; apex other than apiculate. Calyx teeth at most half as long as wide. |
| 10 | Leaves crowded at apices of branchlets, thick-coriaceous; acute to acuminate. Inflorescence branches stout, compact. Fruit ellipsoid, 1½ cm ø |
| 10' | Leaves evenly spread, chartaceous to subcoriaceous; apex caudate (over 1 cm). Inflorescence branches rather slender |
| 11 | Leaves abruptly cuspidate (over 1 cm); nerves arcuate, clearly impressed above. Inflorescence raceme-like, seldom branched more than twice. Petals densely silky outside. Branchlets slender. Fruit oblong, l½ -2 by 0.8-1 cm |
| 11' | Leaves other than abruptly cuspidate; nerves not arcuate but mostly sharply prominent, veins mostly distinct. Inflorescence usually branched twice or more, not terminating into a dichasium. Petals glabrous to appressed hairy. Fruit ovoid to oblong, 2¼-3½ by 1-1¼ cm |
