| 1 | Leaves membranous, often with irregular whitish blotches. Perianth 2-lobed; ovary glabrous. Fruits glabrous, globose, 1.5-2 cm diam.; pericarp 1-2 mm thick; seeds globose. — Riverine or marshy, usually not far from the coast |
| 1' | Leaves of different consistency, generally without whitish blotches. Fruits glabrous or pubescent, globose or ellipsoid; if globose either only 1 cm diam. (H. subtilis), or the pericarp more than 2 mm thick, at least at one side; seeds mostly ellipsoid. — Coastal or not |
| 2 | Twigs angled or ridged. — Aru Is., New Guinea |
| 2' | Twigs terete, sometimes lined in-between the bases of petioles but neither angled nor ridged. — New Guinea to Solomon Is |
| 3 | Leaves with dots beneath (lens!). Perianth 2-lobed. — New Guinea (Bird's Head to W Sepik Prov.) |
| 3' | Leaves without dots beneath |
| 4 | Perianth 3- (or 4-)lobed |
| 4' | Perianth 2-lobed |
| 5 | Ovary glabrous (?). Fruits 10-16 mm long, glabrous. Leaves chartaceous, 7-14 cm long; petiole comparatively long and slender, 11-20 mm long. — SW & S New Guinea (Digul, Western Prov.) |
| 5' | Ovary pubescent. Fruits 17-20 mm long, pubescent at base. Leaves membranous or thinly chartaceous, 10-27 cm long; petiole 7-15 mm. — Papua Barat (Bird's Head) |
| 6 | Flower buds depressed-globose, lobes nearly 1 mm thick; ovary pubescent. Fruits 17-20 mm long, pubescent. Leaves membranous or thinly chartaceous. — Papua Barat (Bird's Head) |
| 6' | Female flowers and fruits not known |
| 7 | Leaves membranous. — SW New Guinea; possibly Aru and Tanimbar Is |
| 7' | Leaves thinly coriaceous. — SW New Guinea (a species close to H. aruana). |
| 8 | Perianth 3- (or 4-)lobed, [cleft almost to the base.] — Papua New Guinea (East Sepik Prov.) |
| 8' | Perianth 2-lobed |
| 9 | Ovary and fruits glabrous |
| 9' | Ovary and fruits pubescent. [Hairs on fruits either distinct or small and inconspicuous and usually only to be seen at the base of the fruits near the insertion of the stalk (lens!). Fruits ellipsoid, sometimes globose in H. sinclairii.] |
| 10 | Leaf bud, twig apex, and inflorescences with hairs 0.3-1.5 mm long. Leaves 17-45 cm long, often ± parallel-sided; nerves 30-40 pairs. [Fruits ellipsoid, 3.4-5.5 cm long, glabrous.] — Moluccas and W & C New Guinea |
| 10' | Leaf bud, twig apex, and inflorescences with hairs 0.2 mm long or less; hairs in H. moluccana and H. tuberculata 0.1-0.3 mm long. Leaves generally smaller; nerves fewer |
| 11 | Fruits globose or subglobose, [not beaked and without pseudostalk], 1.4 cm diam. or less |
| 11' | Fruits ellipsoid, 1.3 cm long or more |
| 12 | Fruits brown on drying; pericarp 1.5-3 mm thick. Buds cleft nearly to the base. — Northern parts of Papua Barat and Papua New Guinea |
| 12' | Fruits blackish on drying; pericarp 1 mm thick. Buds cleft c. 1/3. — Aru Is., whole of New Guinea |
| 13 | Fruits to 2 cm long, blackish on drying; apex pointed/beaked or not, base without or with long or short pseudostalk |
| 13' | Fruits 1.3-3.7 cm long, (dark) brown on drying; apex rounded, base mostly without pseudostalk |
| 14 | Pseudostalk of fruit (1.5-)2-6 mm long. — Papua Barat (Jayapura), Papua New Guinea (W Sepik Prov.) |
| 14' | Pseudostalk absent or up to 3 mm long.—Whole of New Guinea |
| 15 | Buds 2 mm long, cleft 1/2-4/5. Fruits 1.3-2.8 cm long, pericarp 1-2 mm thick. — Moluccas, W New Guinea |
| 15' | Buds 2-3 mm long, cleft 1/2-2/3. Fruits 1.5-3.7 cm long, pericarp 1-8 mm thick. — Papua New Guinea (Milne Bay Prov., Bismarck Archipelago, Papuan Islands) |
| 16 | Leaf bud, twig apex, and inflorescences with hairs 0.2 mm long or less (0.1-0.3 mm long in H. psilantha) |
| 16' | Leaf bud, twig apex, and inflorescences with hairs 0.5-1 mm long (0.2-0.5 mm long in H. ampliformis; indumentum not known in H. ampla) |
| 17 | Hairs 0.1-0.3 mm long. Infructescences and female inflorescences large, much branched, 10-16 cm long. Fruits 1.7-2.2 cm long, pericarp 1-2 mm thick. — Papua New Guinea (Bismarck Archipelago, Bagabag I., Long I.). |
| 17' | Hairs 0.1-0.2 mm long, or less. Infructescences and female inflorescences 10 cm long or less. Fruits variable |
| 18 | Fruits 1.6 cm long or less; pericarp 1-3 mm thick. Buds pubescent |
| 18' | Fruits 1.5 cm long or more; pericarp 2 mm thick or more; if fruit 1.5 cm long, then almost globose and buds glabrous |
| 19 | Fruits at apex rounded, not apiculate; pseudostalk absent |
| 19' | Fruits apiculate; pseudostalk to 5 mm long |
| 20 | Leaves broadly obovate to oblong, 12-20 by 5-11 cm. Pedicel widening to above and gradually passing into the bud. Fruits (including 1 mm long pseudostalk and 2 mm long apiculum) 1.4 by 0.8-0.9 cm, fruiting pedicel 9-14 mm long, distinctly tapering |
| 20' | Leaves elliptic to lanceolate, 4.5-20 by 0.7-6 cm. Pedicel clearly marked off from the bud. Pseudostalk of fruits 1.5-5 mm; fruiting pedicel up to 10 mm long, not or but little tapering |
| 21 | Pseudostalk of fruits 5 mm long. [Fruits excluding pseudostalk but including 2-3 mm long apiculum 1.6-1.7 by 0.9-1 cm.] |
| 21' | Pseudostalk of fruits 1.5-3 mm long |
| 22 | Leaf bud, twig apex, and inflorescences with hairs 0.3 mm. Tertiary venation of leaves below coarse and distinct. [Female flowers not known; fruits not known with certainty; male buds subglobose, with thick perianth.]. |
| 22' | Leaf bud, twig apex, and inflorescences with hairs 0.1-0.2 mm. Tertiary venation generally less distinct. [Male perianth different.] |
| 23 | Fruits excluding the 1.5-2.5 mm long pseudostalk, but including the 0.5-2 mm long apiculum, 1.2-1.5 by 0.8-1 cm. Male buds clearly marked off from the pedicel |
| 23' | Fruits excluding the 1.5-2 mm long pseudostalk, but including the 2 mm long apiculum, 1.3 by 1 cm long. Male pedicel broadening to above and gradually passing into the bud |
| 24 | Buds 2-2.4 mm long, glabrous. Leaves 6-14 cm long. [Fruits (sub)globose, short- ellipsoid, or obovoid, 1.5-2.5 by 1.5-2 cm; pericarp 4-6 mm thick.] — E Papua New Guinea |
| 24' | Buds 2.5 mm long or more, pubescent or glabrescent. Leaves 10 cm long or more |
| 25 | Fruits 1.6-3 cm long, usually with coarse pale wart-like lenticels; (dry) pericarp 2-6 mm thick (sometimes much resembling small-fruited H. pachycarpa). — Moluccas, whole of New Guinea including Bismarck Archipelago; 0-1000 m. |
| 25' | Fruits (3-)3.5-7.5 cm long; pericarp (4-)5 mm thick or more. — New Guinea; (450-) 1000-2000 m |
| 26 | Buds pubescent. Fruits 3-4.5 cm long; pericarp 4-10 mm thick |
| 26' | Buds glabrescent. Fruits 6-7.5 cm long; pericarp 10-20 mm thick |
| 27 | Leaf bud and inflorescences with hairs 0.2-0.5 mm long. Fruits not known. [Leaf bud, female flowers, and fruits not known in H. ampla.] |
| 27' | Leaf bud and inflorescences with hairs 0.5—1(—1.5) mm long. Fruits usually conspicuously pubescent |
| 28 | Inflorescences glabrescent. — Papua New Guinea (Sepik Prov.). |
| 28' | Inflorescences pubescent. — Papua New Guinea (Sepik and Morobe Prov.) |
| 29 | Leaves coriaceous, beneath with harsh hairs, when shed leaving thickened scars. Buds 4 mm long, opening with narrow pore-like slit. [Fruits 3-5 cm long, pericarp 4-7 mm thick.] — New Guinea |
| 29' | Leaves membranous or chartaceous. Buds cleft 1/4-1/2 |
| 30 | Flowers [only the male known] entirely pubescent. [Fruits 2-2.4 cm long, pericarp 4-7 mm thick.] — New Guinea |
| 30' | Flowers largely glabrescent |
| 31 | Leaves generally oblong-lanceolate, at apex caudate. Buds 4 mm long. Fruits 2.5-3 cm long. — Papua New Guinea (New Britain) |
| 31' | Leaves oblong(-lanceolate), at apex not caudate (always?). Buds 3 mm long. Fruits 1.2-2.8 cm long. — Most of Papua New Guinea (incl. New Britain and New Ireland) |
