| 1 | Disk short-cupular, rarely pulvinate and concave above, (partly or completely surrounding the ovary in bisexual flowers), usually 4- or 5-lobed, papillose. Filaments free. |
| 1' | Disk pulvinate, rarely cylindric and torus-like, often reduced and stipe-like, (at the base of ovary in bisexual flowers), usually not lobed, not papillose, rarely obsolete in ♂. Filaments often connate at the base, sometimes free |
| 2 | Stamens 5, 3-5 fertile |
| 2' | Stamens 5 or 4, only 1 (rarely 2) fertile. |
| 3 | Flowers 5-merous, very rarely associated with some 4-merous ones. |
| 3' | Flowers 4-merous, very rarely associated with some 5-merous ones. |
| 4 | Inflorescences usually densely branched and flowered, tomentose. Calyx lobes densely puberulous on both surfaces especially outside |
| 4' | Inflorescences laxly branched and flowered, puberulous or sparsely puberulous, glabrescent, or glabrous. Calyx lobes sparsely puberulous only outside or glabrous. |
| 5 | Inflorescences and calyx lobes puberulous, rarely glabrescent.Pedicels 1½-2½ vnm. Disk pulvinate and concave above. Petals lanceolate. Fruits obliquely subglobose |
| 5' | Inflorescences and calyx lobes glabrous. Pedicels longer, 3-4 mm. Disk short-cupular. Petals narrowly elliptic, or linear. Fruits obliquely oblong |
| 6 | Petals with apical parts of ridges free from the inner surface. |
| 6' | Petals with apical parts of ridges not free from the inner surface. |
| 7 | Free parts of ridges parallel to the surface. Fruits (fresh) yellowish green, globose |
| 7' | Free parts of ridges bent away from the surface. Fruits (fresh) dark purple, broadly ellipsoid |
| 8 | Inflorescences puberulous or pubescent, sometimes glabrescent. Fruits (fresh) 5½-9 by 4-9 cm (but smaller in M. griffithii). |
| 8' | Inflorescences glabrous. Fruits smaller (fresh or dried), 2½-3½ by l ¾-2½ cm (not known in M. gracilipes). |
| 9 | Inflorescences terminal and sometimes also in the apical leaf axils, usually crowded at the apex of the twigs. |
| 9' | Inflorescences axillary only, often in several successive leaf axils |
| 10 | Petals ovate- or elliptic-oblong, 1½-2 mm wide |
| 10' | Petals lanceolate, ⅔-l¼ mm wide. |
| 11 | Ridges on the inner surface of the petals merged only at the very base. Seed not labyrinthine |
| 11' | Ridges on the inner surface of petals merged at the lower 1-2 mm. |
| 12 | Petals with 3 ridges on the inner surface. Seed with transverse lobes or folds (shown on cross-section) |
| 12' | Petals with 3(-5) ridges on the inner surface. Seed with very irregular lobes or folds (shown on cross-section) |
| 13 | Inflorescences terminal sometimes also in the uppermost leaf axil, distinctly paniculate and pyramidal. |
| 13' | Inflorescences terminal and also in the apical leaf axils, crowded at the apex of the twigs, seemingly fasciculate. |
| 14 | Petals lanceolate, 1¼ rnm wide; ridges 3(-5) on the inner surface. Leaves with 8—12 pairs of nerves; apex acuminate |
| 14' | Petals elliptic, rarely ovate, 1½-2½ mm wide; ridges (3-)5(-7) on the inner surface. Leaves with 14-23 pairs of nerves; apex acute or obtuse |
| 15 | Leaves elliptic to elliptic-oblong, obovate-oblong or oblanceolate, (7-)13-19cm long; veins distinct beneath, faint above |
| 15' | Leaves elliptic-lanceolate, 7-10 cm long; veins obscure on both surfaces |
| 16 | Leaves elliptic to narrowly lanceolate, or obovate to oblanceolate, or spathulate, 5-43 by 2-16 cm, leaf-index usually less than 4. |
| 16' | Leaves linear, sometimes linear-lanceolate, rarely spathulate, (9-) 15-60 by (l¼-)3½-5 cm, leaf-index more than (7-)10 |
| 17 | Petals not ridged on the inner surface. Stamens 10: 5 fertile and 5 sterile. |
| 17' | Petals distinctly ridged on the inner surface. Stamens 5: 1 (or 2) fertile, 4 (or 3) imperfect or sterile, or all fertile (M. superba). |
| 18 | Leaves large (usually 27-38 by 12-15 cm); apex mucronate. Flowers reddish or pink. Fertile stamens with one much longer than the others. Fruits ellipsoid |
| 18' | Leaves small (8—18 by 2½-4½ cm); apex obtuse or rounded. Flowers deep violet. Fertile stamens ± equal. Fruits pyriform |
| 19 | Leaves without hair-like fibers shown upon breaking; petiole not flattened. Inflorescences usually glabrous. Petals with 3(-5) ridges confluent at the basal part. |
| 19' | Leaves with hair-like fibers shown upon breaking; petiole flattened. Inflorescences pubescent or tomentose. Petals with only one ridge. |
| 20 | Leaves rigidly coriaceous; apex obtuse, rounded, notched, acute, or mucronate; veins invisible or obscure on both surfaces. |
| 20' | Leaves subcoriaceous, not rigid; apex short-acuminate, acute, rarely obtuse; veins distinct on both surfaces. Fruits dark green, obliquely ovoid or broad-ellipsoid. |
| 21 | When fresh: Inner surface of petals pinkish. Ovary ochraceous. Fruits obliquely ovoid, yellowish or greyish green, smooth |
| 21' | When fresh: Inner surface of petals purple. Ovary white. Fruits broadly ovoid or globose, brownish, roughish |
| 22 | Petals 5-8 mm long. Fertile stamens 1 (or 2) |
| 22' | Petals 20-25 mm long. Fertile stamens 5 |
