| 1 | Leaves membranous, usually with irregularly shaped whitish blotches. Fruits globose, 1.5-2 cm diam., glabrous; pericarp 1-2 mm thick; seeds globose. [Perianth 2-lobed; ovary glabrous.] — Plants usually growing not too far from the coast. |
| 1' | Leaves variable, usually not white-blotched. Fruits subglobose or ellipsoid; seeds ellipsoid. — Plants coastal or not |
| 2 | Perianth 2-lobed |
| 2' | Perianth predominantly 3- (or 4-)lobed |
| 3 | Leaves coriaceous, densely short-pubescent and with dots beneath (lens!). Twigs grey-brown, not contrasting with petioles |
| 3' | Leaves membranous, glabrous and without dots beneath. Twigs greyish or straw- coloured, contrasting with blackish petioles |
| 4 | Inflorescences ± spike-like, 5-10 cm long. Perianth persistent under the fruits (always?). — Borneo (SE Sabah) |
| 4' | Inflorescences branched, 1-2 cm long. Perianth not persistent under the fruits. — Borneo (Sarawak, Sabah, E, C & S Kalimantan). |
| 5 | Leaves in 3 or more rows along the twigs |
| 5' | Leaves distichous |
| 6 | Leaves ± clustered at the apex of the twigs. Petiole proportionally long and slender, 25-50 mm long. — Northern Borneo; sandy soils |
| 6' | Leaves not clustered. Petiole proportionally shorter |
| 7 | Leaves 10-30 cm long. Twigs pale, grey or straw-coloured, contrasting with the blackish petioles. Buds 2.5-3 mm long. Fruits 1.5-6 cm long |
| 7' | Leaves 20-45 cm. Twigs brown, not contrasting with the petioles. Buds 4-5 mm long. Fruits 6-8 cm long |
| 8 | Twigs lined or ridged |
| 8' | Twigs terete or faintly angular, neither distinctly lined nor ridged |
| 9 | Leaves with (sub)persistent indumentum beneath (sometimes largely glabrescent in H. wallichii) |
| 9' | Leaves glabrous or early glabrescent beneath (midrib sometimes late glabrescent) |
| 10 | Plant stout; leaves 50 cm long, petiole 3 mm long only. — Borneo (lowland Sarawak) |
| 10' | Plants variable in habit; leaves large, but petiole proportionally much longer.11 11a. Older leaves with scabrous hair scars above and beneath. Fruits 1-1.4 cm long. |
| 10'' | Leaves not scabrous. Fruits larger |
| 11 | Leaves with dots and/or dashes beneath (lens!) |
| 11' | Leaves with or without dots beneath, never with dashes |
| 12 | Flower buds with persistent indumentum; fruits without persistent perianth |
| 12' | Buds glabrous or early glabrescent; fruits with persistent perianth or not. |
| 13 | Ovary pubescent; fruits sometimes pubescent only towards the base |
| 13' | Ovary and fruits glabrous |
| 14 | Twigs 3.5-5 mm diam. Leaves 10-23 cm long; nerves 11-16 pairs. Fruits largely glabrescent; perianth not persistent |
| 14' | Twigs 4-7 mm diam. Leaves 18-45 cm long, nerves 18-25 pairs. Fruits pubescent, with persistent perianth |
| 15 | Twigs 3-6 mm diam. Leaves 18-35 cm long; upper surface sometimes bullate; [nerves 17-20 pairs.] Fruits 2.3-2.7 cm long |
| 15' | Twigs 1.5-3 mm diam. Leaves often smaller, not bullate. Fruits 1-1.5 cm long 17 17a. Leaves membranous, beneath without dots; nerves 14-17 pairs. |
| 15'' | Leaves thinly chartaceous, beneath with dots; nerves 5—9(—11) pairs |
| 16 | Leaves with dots or with dots and dashes beneath (lens!) (dots not to be confused with smaller, irregularly spaced points, which are usually present) |
| 16' | Leaves without dots beneath (enlarged hair scars sometimes present) |
| 17 | Leaf bud, twig apex, and young inflorescences with hairs 0.2 mm long or more |
| 17' | Leaf bud, twig apex, and young inflorescences with hairs 0.1 mm long or less 21 20a. Twigs hollow. Leaves often with persistent indumentum beneath. Pedicel not articulated. Fruits with persistent perianth |
| 17'' | Twigs (almost) solid. Leaves glabrescent beneath. Pedicel articulated. Fruits without persistent perianth |
| 18 | Twigs pale, grey-brown or yellowish, contrasting with the dark brown petioles |
| 18' | Twigs brown on drying, ± not contrasting with the petioles |
| 19 | Leaves membranous, (blackish) brown above, somewhat paler beneath. Perianth persistent under the fruits. — Mixed forest |
| 19' | Leaves usually chartaceous, bright brown or olivaceous above. Perianth not persistent under the fruits |
| 20 | Twigs 2-3 mm diam. Leaves 7-16 cm long, bright brown or chocolate beneath, contrasting with the grey-olivaceous upper surface. Fruits 1.8-2.7 cm long. — Kerangas, peat forest |
| 20' | Twigs 3-10 mm diam. Leaves 13-35 cm long, the lower surface not conspicuously contrasting with upper surface |
| 21 | Fruits 5 cm long or more. Leaves not conspicuously matt above. 21. H. discolor b. Fruits 2 cm long or less. Leaves matt, caused by finely wrinkled upper surface. |
| 22 | Leaves (elliptic-)oblong. Fruits 1.6-2 cm long. — Heath forest, peat swamp forest |
| 22' | Leaves elliptic-oblong to lanceolate. Fruits 1.5 cm long. — Mixed forest |
| 23 | Leaf bud and immature inflorescences with hairs 0.1 mm long or less. Lateral nerves flat or sunken, or but little raised above |
| 23' | Leaf bud and immature inflorescences with hairs 0.1 mm long or more; lateral nerves above raised or not; if hairs only 0.1 mm long, then the lateral nerves above distinctly raised, at least in the lower half |
| 24 | Species from lowland limestone, up to c. 700 m. Leaves membranous. Fruits not known. — Borneo (NE Kalimantan) |
| 24' | Montane species; 800-1800 m. Leaves membranous or coriaceous. Fruits 5 cm long or less. — Borneo (Sarawak, Sabah) |
| 25 | Leaves without distinct large hair scars beneath (lens!). Fruits 3-5 cm long. |
| 25' | Leaves with (usually) distinct yellowish enlarged hair scars beneath. Fruits 3.5-5 cm long |
| 26 | Pedicel not articulated (best seen in male flowers). Fruits with perianth persistent or not |
| 26' | Pedicel articulated. Perianth not persistent under the fruits |
| 27 | Leaves 15-45 cm long. Fruits 6 cm long or more; perianth ± persistent. — Lowland or montane forest |
| 27' | Leaves 5-20 cm long. Fruits 2-4 cm long; perianth not persistent. — Montane forest at 800-2000 m |
| 28 | Nerves 11-22 pairs. — Borneo (Sabah: Mt Kinabalu); 1000-1500 m |
| 28' | Nerves 20-30 pairs. — Forests up to c. 1000 m |
| 29 | Female flowers and fruits not known. — Hallier 624, Mt Damoes, W Kalimantan; probably an undescribed species close to H. valida, see there. |
| 29' | Perianth 4-5 mm long. Fruits 6-8 cm long, pericarp 10-20 mm thick |
| 30 | Leaves membranous, apex acute-acuminate. Fruits 2.4-3 cm long |
| 30' | Leaves chartaceous or coriaceous, apex rounded to (sub)acute, not acute-acuminate |
| 31 | Leaves chartaceous or coriaceous, without large hair scars beneath (lens!). Perianth 2 mm long. Fruits 2-2.7 cm long |
| 31' | Leaves usually strongly coriaceous, usually with large hair scars beneath. Perianth 2.5-3 mm long. Fruits 3-4 cm long |
| 32 | Male inflorescences very stout, the rachis towards the base 5-8 mm diam. [Female inflorescences, flowers, and fruits not known.] — Borneo (W Kalimantan) |
| 32' | Male inflorescences less stout |
| 33 | Midrib on upper leaf surface towards the transition to the petiole 3 mm broad or more |
| 33' | Midrib at base narrower |
| 34 | Leaves 16-28 cm long, base rounded or short-attenuate; nerves 16-19 pairs. — Borneo (Sarawak) |
| 34' | Leaves 5-28 cm long, base rounded, short-, or long-attenuate; nerves 5-15(-20) pairs |
| 35 | Lateral nerves sunken, flattish, or but slightly raised above |
| 35' | Lateral nerves raised above |
| 36 | Leaf apex rounded. Fruits not seen |
| 36' | Leaf apex acute-acuminate. Fruits 1.5-2 cm long |
| 37 | Leaf bud and young inflorescences with hairs 0.1-0.2 mm long. Leaves on drying dull, greyish brown, colour of upper and lower surface not much contrasting. Fruits 1.7-2 cm long |
| 37' | Leaf bud and young inflorescences with hairs 0.2 mm long or more; if hairs 0.1 mm long, then the olivaceous to dark-brown upper leaf surface much contrasting with the cinnamon colour beneath |
| 38 | Twigs 1-3 mm diam. Leaves membranous, 10—18(—27) cm long. Fruits 2.3-2.4 cm long |
| 38' | Twigs 2-5 mm diam. Leaves chartaceous; leaves and fruits of variable sizes. |
| 39 | Twigs early glabrescent; bark ± longitudinally cracking. Leaf apex long acute- acuminate. Fruits 2.8-3.2 cm long; pericarp hard-woody, 8-10 mm thick. — Borneo (Brunei) |
| 39' | Twigs late glabrescent; bark striate, not cracking. Leaf apex acute-acuminate, the acumen not conspicuously long. Fruits 1.9-6 cm long. — Variable, with 3 varieties (based on fruit size). Whole of Borneo |
