| 1 | Leaf blade foliolate (sometimes partly or all simple) |
| 1' | Leaf blade simple (unlobed or lobed) |
| 2 | Plant slender, 2-5 m high. Leaf blade 3 foliolate, chartaceous; probract membranous, flat (sometimes caducous). Tendrils simple or 2-branched. Fruit 6-9 cm long |
| 2' | Plant stouter. Leaf blade 3-5 foliolate, coriaceous; probract chartaceous, incurved-concave. Tendrils 2- or 3-branched. Fruit more than 10 cm long |
| 3 | Leaf blade unlobed. [Leaf blade subcircular or ovate, margin entire, minute sparse dents excepted.] |
| 3' | Leaf blade lobed |
| 4 | Blade margin ± recurved |
| 4' | Blade margin flat |
| 5 | Leaf blade (usually) minutely hairy beneath, at least along the veinlets |
| 5' | Leaf blade glabrous beneath |
| 6 | Veinlets raised beneath |
| 6' | Veinlets not or but little raised beneath |
| 7 | Leaf blade chartaceous, ovate; venation ± raised, distinct. Seeds 8-10 mm long. — Siberut Is. |
| 7' | Leaf blade ± membranous; venation flat, faint beneath. Seeds 15-20 mm long |
| 8 | Leaf blade subcircular |
| 8' | Leaf blade ovate-hastate |
| 9 | Plant with fruit (and female flowers) |
| 9' | Plant with male flowers |
| 10 | Fruit ovoid. Seeds tumid |
| 10' | Fruit globose, ellipsoid, (ob)ovoid, or long-cylindrical. Seeds compressed |
| 11 | Fruit pulp not fibrous. Seeds ± fusiform (barrel-shaped) (Fig. 91b) |
| 11' | Fruit pulp fibrous. Seeds butterfly-shaped with inflated lateral parts. (Lobed leaf blades not seen in Sumatra) |
| 12 | Seed margin undulate or coarsely notched. Fruit ± ellipsoid, 2.5-5 cm long, or long-cylindrical in cultivated var. anguina |
| 12' | Seed margin entire. Fruit globose, ellipsoid, or (ob)ovoid |
| 13 | Fruiting pedicel with 2 parts with differing surface colour and texture |
| 13' | Fruiting pedicel evenly coloured |
| 14 | Fruit ellipsoid. Seeds notched at one end |
| 14' | Fruit globose. Seeds not notched |
| 15 | Fruit (sub)globose |
| 15' | Fruit longer than wide |
| 16 | Fruiting pedicel thick, 10-20 mm thick |
| 16' | Fruiting pedicel c. 5 mm thick |
| 17 | Tendrils simple. Fruit globose, 5.5-12 cm diameter |
| 17' | Tendrils 2- or 3-branched. Fruit ellipsoid, more than 10 cm diameter |
| 18 | Leaf blade deeply 3-5-lobed. Seeds 3-4 mm thick, base and apex rounded |
| 18' | Leaf blade shallowly 5-lobed or ± 5-angular. Seeds 1-2 mm thick, chisel-shaped pointed at base |
| 19 | Fruit more than 10 cm long; fruiting pedicel c. 10 mm thick |
| 19' | Fruit less than 10 cm long; fruiting pedicel 5 mm thick or less |
| 20 | Pericarp thin, less than 5 mm thick. Seeds (narrowly or) broadly ovate, 15-20 mm long, 2-3 mm thick |
| 20' | Pericarp thick, c. 5 mm or more. Seeds obovate, 10-13 mm long, less than 2 mm thick |
| 21 | Leaf blade hairy beneath. Stem and leaf blade in young state reddish, reddish brown on drying. Probract narrowly elliptic or linear |
| 21' | Leaf blade glabrous. Stem and leaf blade green, (dark) brown on drying. Probract obovate or elliptic |
| 22 | Bracts 1(-2) mm long, often caducous (including cultivated var. anguina) |
| 22' | Bracts more than 2 mm long |
| 23 | Rachis 1-2 mm thick |
| 23' | Rachis 2-10 mm thick |
| 24 | Persistent basal part of pedicel (1-)2-15 mm long. Leaf blade beneath finely hairy, at least along the veins |
| 24' | Persistent basal part of pedicel usually (nearly) absent. Leaf blade scabrous |
| 25 | Rachis of raceme 5-10 mm thick |
| 25' | Rachis of raceme 2-5 mm thick |
| 26 | Tendrils simple. Bracts membranous, with short soft yellowish hairs, margin entire |
| 26' | Tendrils 3-branched. Bracts chartaceous, with minute brown hairs, apical part coarsely dentate |
| 27 | Younger parts of shoots reddish tinged on drying |
| 27' | Whole plant green, brown, or blackish on drying |
| 28 | Leaf blade glabrous. Petals white |
| 28' | Leaf blade hairy beneath. Petals with pinkish veining and/or fringes |
| 29 | Leaf blade ± 5-angular, with several minute glands close to the insertion of the petiole. Bracts entire. [Sepals with slender sidelobes.] |
| 29' | Leaf blade (deeply) 3-5 lobed, c. 1/3 or deeper; glands fewer, not close to the insertion of the petiole. Bracts dentate |
| 30 | Leaf blade 3-lobed to c. 1/2-way deep, lobes ± ovate-triangular. Bracts without glands |
| 30' | Leaf blade deeply 5-lobed, lobes narrowly ellipsoid. Bracts with glands |
| 31 | Probract ± elliptic, c. 4 mm long. [Seeds notched at apex] |
| 31' | Probract narrowly elliptic, 5-18 mm long. [Seeds ± rounded at both ends] |
