| 1 | Flower buds pubescent at base. [Ovary pubescent. Fruits ellipsoid, 2.5 — 4 cm long, pubescent. In male the flowers in dense clusters, strongly fragrant.] — Cultivated, originating from Sri Lanka |
| 1' | Buds glabrous (pubescent at base in H. hirtiflora and H. triandra) |
| 2 | Leaves membranous, often with irregular whitish blotches. Fruits globose, 1.5-2 cm diam., glabrous; pericarp 1-2 mm thick; seeds globose. [Perianth 2-lobed; ovary glabrous.] — Riverine or marshy, usually near the coast |
| 2' | Leaves of different consistency, usually not blotched. Fruits and seeds ellipsoid. — Plant not coastal |
| 3 | Perianth 2-lobed. Leaves with dots beneath (dots not to be confused with smaller punctation of different origin, lens!) |
| 3' | Perianth 3- (or 4-)lobed. Leaves with or without dots beneath |
| 4 | Leaves coriaceous, 10-20(-28) cm long, finely pubescent beneath. Twigs 2-6 mm diam. Fruits 1.5-2.2 cm long, with persistent perianth. — Peat swamp or padang forest |
| 4' | Leaves membranous or thinly chartaceous, 5-12 cm long, glabrous beneath. Twigs 1.5-2 mm diam. Fruits 1-2 cm long; perianth not persistent. — Mixed forest. |
| 5 | Ovary and fruits (at least at base) pubescent. Leaves with persistent indumentum beneath |
| 5' | Ovary and fruits glabrous (fruits almost glabrous in H. triandra). Leaves glabrous or pubescent beneath |
| 6 | Twigs 2-5 mm diam. Leaves 9-27 cm long, lower surface without dots. Fruits with hairs 0.5 mm long or less. — Thailand, Peninsular Malaysia; specimens from Sumatra not seen |
| 6' | Twigs 5-8 mm diam. Leaves 20-36 cm long, with dots beneath (lens!). Fruits with hairs 2 mm long |
| 7 | Leaves with dots beneath (lens!). Lateral nerves generally flat or sunken above |
| 7' | Leaves without dots beneath. Nerves either raised or flat to sunken above. |
| 8 | Leaves usually with persistent indumentum beneath (sometimes glabrescent), and with both dots and dashes (lens!). Twigs conspicuously hollow. Fruits 4-7 cm long, the perianth generally persistent |
| 8' | Leaves glabrous or glabrescent beneath, with dots, not with dashes. Twigs not conspicuously hollow. Fruits variable |
| 9 | Bark of twigs pale, greyish to straw-coloured, contrasting with blackish petiole. Leaves dispersed in 3-5 rows. [Female flowers and fruits not known.] — Sumatra (N Aceh); at c. 1300 m |
| 9' | Bark of twigs brown, not contrasting with petiole. Leaves distichous (or in 3 rows in H. glabra, p.p.) |
| 10 | Fruits (4.5-)5-8 cm long, pericarp 10-20 mm thick |
| 10' | Fruits 1-2.5 cm long, pericarp much thinner |
| 11 | Twigs 1.5-2 mm diam. Leaves 5-12 cm long. Fruits 1.1-2 cm long |
| 11' | Twigs 2.5-4(-6) mm diam. Leaves (8-) 12 cm long or more. Fruits 1.8-2.5 cm long |
| 12 | Leaves distichous. — C & N Sumatra |
| 12' | Leaves distichous or in 3 rows. — S Sumatra, Mentawai Is., north to Simeulue I., Java |
| 13 | Leaves with persistent indumentum beneath. Fruits with persistent perianth. |
| 13' | Leaves glabrous or glabrescent beneath. Fruits with persistent perianth or not |
| 14 | Hairs harsh, older leaves scabrous beneath. [Fruits 1-1.4 cm long.] |
| 14' | Hairs softer; older leaves not scabrous beneath |
| 15 | Twigs 5-8 mm diam.; leaves 20-40(-70) cm long. Leaf bud with hairs 0.5-1 mm. Fruits 3.8-5.5 cm long |
| 15' | Twigs 3-5 mm diam.; leaves 13-21 cm long. Leaf bud with hairs 0.2-0.3 mm long. Fruits 2-3 cm long |
| 16 | Lateral nerves flat or sunken or but faintly raised above. Colour of lower leaf surface generally greyish brown, not much contrasting with upper surface |
| 16' | Lateral nerves distinctly raised above. Colour of the lower leaf surface bright brown or chocolate, contrasting with the upper surface |
| 17 | Twigs 1.5-3 mm diam. Leaf bud, twig apex, and young inflorescences with woolly hairs 0.3-0.7 mm. Leaves 5-9 cm long |
| 17' | Twigs (2-)3-10 mm diam. Leaf bud, twig apex, and inflorescences 0.1-0.3 mm long. Leaves more than 10 cm long |
| 18 | Leaves distichous, matt on drying caused by minutely wrinkled upper surface. Bark of twigs straw or brown |
| 18' | Leaves distichous or in 3-5 rows; not particularly matt, upper surface not finely wrinkled. Bark of twigs pale, grey-brown or straw, contrasting with the blackish petiole |
| 19 | Leaves elliptic-oblong to oblong, olivaceous-brown above. Stem grey-brown, not much contrasting with petiole. Fruits brown on drying, 2.2-3 cm long, perianth persistent |
| 19' | Leaves elliptic-oblong to lanceolate, dark olivaceous above. Stem pale, ± yellowish brown, rather contrasting with the petiole. Fruits blackish on drying, 1.5 cm long, perianth not persistent |
| 20 | Leaves distichous or in 3 rows. Fruits 2.5-3.5 cm long, with the perianth persistent. Pedicel articulated (best seen in male flowers). |
| 20' | Leaves in 3-5 rows. Fruits 3-5.5 cm long, perianth not persistent. Pedicel not articulated |
| 21 | Perianth 4-lobed. Pedicel not articulated. Fruits 8-9 cm long. [Flowers known only from the remnants persistent under the young fruits.] |
| 21' | Perianth generally 3-lobed. Pedicel articulated. Fruits up to 6.5 cm long. |
| 22 | Twigs ± angular, with lines or ridges |
| 22' | Twigs terete or faintly angular, neither lined nor ridged |
| 23 | Buds pubescent (known only in male flowers). Fruits 5-6 cm long. — N Sumatra |
| 23' | Buds glabrous. Fruits 2-4 cm long |
| 24 | Twigs 1-3 mm diam. Leaves membranous, midrib beneath late glabrescent. Fruits 2.3-2.4 cm long |
| 24' | Twigs 2-5 mm diam. Leaves chartaceous. Fruits 1.9-6.5 cm long |
| 25 | Leaf bud and inflorescences with hairs 0.1-0.2 mm long. Midrib beneath early glabrescent. Fruits 4.5-6.5 cm long |
| 25' | Leaf bud and inflorescences with hairs 0.1-0.6 mm long. Midrib often late glabrescent. Fruits 1.9-3.5 cm long. — Variable; 3 varieties based on fruit size |
