1. Inflorescences on trunk or restricted to base of trunk ........................................................................ 2 – Inflorescences in leaf axils, or on twigs behind leaves (sometimes on branches) .............................. 6
2. Inflorescences borne on slender, flexible, branched basal flagellae ........................... M. hypogaeum – Not so ................................................................................................................................................ 3
3. Inflorescences on stout, sparsely branching axes to at least 7 cm long ....................... M. praestigiosum
– Inflorescences on woody tubercles or much-branched axes less than 7 cm long ............................... 4
4. Inflorescences on woody tubercles .............................................................................. M. anomalum – Inflorescences on much-branched axes ............................................................................................. 5
5. Leaves with 8–10 pairs of lateral nerves. Outer petals to 2.5 cm long, 0.5 cm wide. Monocarps with blunt beak ...................................................................................................................... M. borneense
– Leaves with c. 20 pairs of lateral nerves. Outer petal to 7 cm long, 2.5 cm wide. Monocarps with hard, sharp beak ................................................................................................................ M. congregatum
6. Leaves membranous. Inflorescences axillary, few-flowered (generally more than one). Sepals more than 8 mm long. Monocarps globose to ellipsoidal with rounded to slightly blunt apex ..................... ............................................................................................................................ M. membranifolium
– Leaves chartaceous to coriaceous. Inflorescences single to multi-flowered but if few-flowered and axillary then with sepals to 6 mm long. Monocarps ellipsoidal with blunt to beaked apex .............. 7
7. Young flowers with conical ‘bud’ stage; sepals more than 6 mm wide ............................................. 8 – Young flowers not with a conical ‘bud’ stage; sepals less than 6 mm wide ...................................... 11
8. Leaves with generally more than 20 pairs of lateral nerves. Flower pedicels more than 2.5 cm long .... ................................................................................................................................... M. macranthum – Leaves with up to 20 pairs of lateral nerves. Flower pedicels to 1 cm long ...................................... 9
9. Twigs densely tomentose. Leaves with dense hairs on nerves below. Flower pedicel to 12 mm long ... ............................................................................................................................................ M. fuscum
– Twigs glabrescent. Leaves glabrous to glabrescent beneath. Flower pedicel generally more than 12 mm long ...................................................................................................................................... 10
10. Leaves to 17 cm long, 7 cm wide. Sepals much broader than long. Monocarps woolly hairy, apex rounded ............................................................................................................................ M. cupulare
– Leaves generally more than 17 cm long, 7 cm wide. Sepals about as long as broad. Monocarps not woolly hairy, apex beaked .................................................................................... M. magnoliiflorum
11. Petals distinctly longitudinally nerved. Monocarps subsessile, pale tomentose ....... M. pachyphyllum – Petals not longitudinally nerved. Monocarps stipitate, glabrous to tomentose ............................... 12
12 (Leaves more than 24 cm long, 7 cm wide). Flowers borne distichously on sparsely branched hairy axes to 2 cm long, 4 mm thick. Petals thick and fleshy. Monocarps with stipe to 14 mm long, shorter than seed-bearing portion ........................................................................................... M. malayanum
– (Leaves generally smaller). Flowers borne in fascicles or on very short and relatively slender axes. Petals relatively thin. Monocarps with stipe generally exceeding length of seed-bearing portion ... 13
13. Flowering pedicel c. 0.5 mm thick; sepals to 2 mm long; petals to 3 mm wide .............. M. asteriellum – Flowering pedicel at least 1 mm thick; sepals more than 2 mm long; petals 4 mm wide or more ... 14
14. Petals 4–5 mm wide. Monocarps densely short brown tomentose, stipe attachment eccentric. .............. ............................................................................................................................... M. xanthopetalum – Petals 8 mm or more wide. Monocarps more or less glabrous, stipe attachment not eccentric ........ 15
15. Outer petals obovate (widest above midway), claw and blade distinct ........................................... 16
– Outer petals lanceolate to oblong-linear (widest at or below midway), little distinction between claw and blade ......................................................................................................................................... 17
16. Leaves obovate, reticulations obscure from above ..................................................... M.hookerianum – Leaves elliptic, reticulations distinct from above ............................................................ M. glabrum
17. Leaves generally less than 20 cm long and 5 cm wide; lateral nerves 9–13 pairs. Sepals 3–4 mm long .. ................................................................................................................................. M. sclerophyllum
– Leaves generally more than 20 cm long and 5 cm wide; lateral nerves 14–15 pairs. Sepals to 3 mm long............................................................................................................................. M. lateriflorum