| 1 | Leaves cordate or auricled, or subcordate (sometimes slightly truncate, rarely obtuse, or cuneate) at the base; petiole obscure, 0-1¼ cm. |
| 1' | Leaves usually cuneate to attenuate (rarely obtuse or slightly subcordate) at the base; petiole distinct, usually 1½-8 cm (¾-1¼ cm in M. minutiflora). |
| 2 | Lower surface of leaves pubescent especially on nerves and veins; distinctly papillose. Drupe with dense, rusty-hairy processes (insect-gall-like) |
| 2' | Lower surface of leaves glabrous; not papillose. Drupe without processes as above |
| 3 | Leaves glabrous on both surfaces. |
| 3' | Leaves densely or sparsely hairy on the lower surface, sometimes glabrescent but then always remaining sparsely hairy on the midrib and nerves. |
| 4 | Inflorescences axillary only, shorter than the petiole. Hypanthium 3-4 mm long. Papillae distinct on the lower leaf surface. Drupe broadly ellipsoid, or ovoid, 3 by 2 cm, apex apiculate. |
| 4' | Inflorescences terminal and axillary (rarely axillary only on ♀), much longer than the petiole. Hypanthium less than 2¼ mm long. |
| 5 | Lower surface of leaves with very distinct papillae. (Branchlets whitish. Drupe unknown) |
| 5' | Lower surface of leaves not papillose, or with very compact, obscure papillae (rarely fine and compact on young leaves in M. castaneifolia). |
| 6 | Inflorescences with large bracts (7-8 mm long). Petals 4-4½ mm long. Ovary flat and round, c. 2½ mm ø. Stomata invisible on lower leaf surface. Drupe subglobose, 2-2½ by 1½-2 cm, apex rounded |
| 6' | Inflorescences with small or minute bracts (⅔-4 mm long). Petals 1½-3 mm long. Ovary sub-globose or globose, c. 1 mm ø. Stomata visible on the lower leaf surface. |
| 7 | Petiole puberulous at the lower ½-1½ cm. Drupe ellipsoid or ovoid, 2 by 1-1¼ cm, apex acute |
| 7' | Petiole glabrous. |
| 8 | Branchlets brown or dark brown, pubescent. Leaves brown to reddish brown and shining above. Filament of the stamen brown. Drupe broadly ellipsoid, 1½ by 1 cm, apex obtuse |
| 8' | Branchlets light yellowish white or light greyish, glabrous. Leaves usually yellowish green and shining above. Filament of the stamen whitish at the apical part. Drupe unknown |
| 9 | Leaves bullate above; veins scalariform. Drupe thickly velvety; indumentum c. 3½ mm thick |
| 9' | Leaves not bullate, almost flat above. Veins reticulate or reticulate-scalariform. Drupe thinly velvety; indumentum less than 1¼U mm thick. |
| 10 | Leaves with densely reticulate-scalariform venation prominent on the lower surface. Lower ½-1½ mm of the filaments united with the petals. Drupe broadly ellipsoid or ovoid, 1½-2½ by 1¼-2¼ cm, apex obtuse |
| 10' | Leaves with loosely reticulate or reticulate-scalariform venation slightly elevated or obscure on the lower surface. Filaments free from the petals (except in M. beccariana). |
| 11 | Leaves not papillose on the lower surface. Flowers small, 2-2½ mm long. Drupe subglobose, c. 1¼ cm Ø |
| 11' | Leaves distinctly papillose on the lower surface. Flowers larger, 3½-9(-12) mm long. |
| 12 | Lower surface of leaves with papillae in prominent groups (often horse-shoe-shaped), separated by broad bands of veins and veinlets. Inflorescences axillary only. Drupe broadly ellipsoid or subglobose, 2¾-3 by 2-2½ cm |
| 12' | Lower surface of leaves with rather uniformly distributed papillae. Inflorescences terminal, or terminal and axillary. |
| 13 | Flowers (5-)7-9(-12) mm long. Lower ¾-1½ mm of filaments laterally united with the petals; ovary almost completely immersed in the receptacle. (Drupe broadly ellipsoid or ovoid 2½-3 by 1¼-2¼ cm) |
| 13' | Flowers 3½-7 mm long. Filaments free. Ovary not immersed in the receptacle. |
| 14 | Hypanthium c. ½ mm long. Anthers c. 1 mm long. Abortive pistil in ♂ minute, glabrous. Drupes ovoid or ellipsoid, l-l¾ mm ø, indumentum ⅔ mm thick. |
| 14' | Hypanthium longer, ¾-2¼ mm long. Anthers ½-¾ mm long. |
| 15 | Leaves tomentose on the lower surface, especially dense on midrib and nerves. Abortive pistil in ♂ 0, replaced by a tuft of hairs. Drupe globose or subglobose, 2¾-3 cm ø, indumentum c. 1/6 mm thick |
| 15' | Leaves sparsely hairy on the lower surface, usually glabrescent except on midrib and nerves. |
| 16 | Hypanthium 1¾-2¼ mm long. Abortive pistil in ♂ conical, ½ mm long, hairy. Drupe broadly ellipsoid, 1½-2½ cm ø, indumentum c. 1/6 mm thick. |
| 16' | Hypanthium ¾-l mm long. Abortive pistil in ♂ minute or 0, glabrous. Drupe broadly ovoid, 2-2¾ cm ø, indumentum c. ⅓ mm thick |
