| 1 | Flowers or fruit in panicles or racemes, however sometimes much reduced. Ovary somewhat superior, at apex flat, broad, not constricted. Styles 3. Fruit becoming dry, dehiscent with valves in truncate apex (indehiscent in Gynostemma, p.p.). Tendrils 2-branched at apex. |
| 1' | Flowers or fruit solitary or fascicled, or in racemes, or panicles. Ovary inferior, at apex narrow, constricted. Style 1. Fruits usually berry-like (pepo-fruit), usually indehiscent. Tendrils unbranched or branched at or below the middle (distally 2-branched in Siraitia and Baijiania). |
| 2 | Climber to 30 m long. (Ovary half-globose, 5-10 mm diam. in Alsomitra). Fruit 20-30 cm long. Seeds c. 2 cm diam., winged |
| 2' | Small or medium climber to 15 m long. Fruit much smaller. Seeds large (Zanonia) or smaller |
| 3 | Fruit half-globose mitriform, 20-30 cm diam. Seed entire, broadly butterfly-like winged, c. 10 cm wide. Flowers creamy |
| 3' | Fruit claviform-cylindric, bluntly triangular, 8-10 cm wide. Seed toothed, with circular wing c. 5 cm wide. Flowers red (female flowers not known) |
| 4 | Ovary and fruit subglobose. Fruit 8 mm diam. or less, dehiscent or indehiscent. Seeds few, not winged |
| 4' | Ovary and fruit elongated. Fruit 1.5 cm long or longer, dehiscent. Seeds mostly winged |
| 5 | Sepals 3, petals 5. Fruit c. 8 cm long. Seeds large, 1.5-2 cm long, winged at both ends, including the wings 4-8 cm long |
| 5' | Sepals and petals 5. Fruit c. 8 cm long or shorter. Seeds shorter |
| 6 | Blade margin serrate. Fruit with 3 horn-like processes at apex. Seeds not winged or winged all around (broadest at the ends). Pedicel often with 1 or 2 small tendril(s). — East Malesia |
| 6' | Blade margin entire. Fruit without horn-like processes at apex. Seeds winged at one side. Pedicel without tendril(s). — West & East Malesia |
| 7 | Sepals much longer than petals. — Moluccas: Morotai Is |
| 7' | Sepals shorter than petals |
| 8 | Fruit (or ovary) ornamented with ridges, warts, or (few) (soft) spines, (irregular) grooves, or fruit fenestrate (fruit of Momordica clarkeana and M. denticulata almost smooth) |
| 8' | Fruit not ornamented (colour or fine texture excepted), surface glabrous or hairy |
| 9 | Fruit ± curved. — Introduced from America, cultivated or locally naturalized |
| 9' | Fruit not curved |
| 10 | Tendrils 3- or more-branched |
| 10' | Tendrils unbranched or 2-branched |
| 11 | Fruit longitudinally ridged |
| 11' | Fruit smooth, or ± bullate, or grooved |
| 12 | Fruit pear-shaped, 10-15 cm long. Seed one |
| 12' | Fruit globose, ellipsoid or pyriform, small or large. Seeds numerous |
| 13 | Fruit (globose or) broadly ellipsoid, c. 10 cm diam. or more, warted (tubercled) or spiny all over. Seeds c. 15 mm long or more, flat, margin cogwheel-like undulate |
| 13' | Fruit (narrowly) ellipsoid or oblong, usually < 10 cm diam. Seeds generally smaller |
| 14 | Tendrils unbranched. Fruit echinate or aculeate-tubercled, or smooth, green or yellow. Seeds oblong, not ornamented, edge smooth |
| 14' | Tendrils unbranched or 2-branched. Fruit tubercled, ribbed or fenestrate, ± beaked. Seeds ornamented or with grooved margin |
| 15 | Fruit not squirting. Flowers yellow 10 |
| 15' | Fruit squirting. Flowers white. [Fruit occasionally smooth, not ornamented.] |
| 16 | Fruit green or yellow, fenestrate, hardly beaked |
| 16' | Fruit orange or red, beaked |
| 17 | Tendrils (unbranched or) 2-branched. Fruit low-ribbed. Seeds ± oblong, margin entire |
| 17' | Tendrils unbranched. Fruit ribbed or (few-)tubercled. Seeds ellipsoid-globose, edge undulate |
| 18 | Plant cultivated (but frequently also found running wild) |
| 18' | Plant wild (some wild species occasionally cultivated; Cayaponia naturalized in Java; Melothria widely naturalized) |
| 19 | Ripe dry fruit opening with apical operculum |
| 19' | Fruit without apical operculum |
| 20 | Fruit frequently ± flask-shaped constricted. Petiole with 2 glands at apex |
| 20' | Fruit (depressed) globose, ellipsoid, or oblong. Petiole without glands at apex |
| 21 | Leaf blade more or less pinnately (veined and) lobed. Seeds brown or black |
| 21' | Leaf blade palmately (pedately) veined, unlobed or lobed. Seeds pale brown or whitish |
| 22 | Tendrils unbranched |
| 22' | Tendrils 2-5-branched |
| 23 | Probract distinct, hooded. Seeds c. 10 mm long, almost unmargined |
| 23' | Probract absent or not obvious. Seeds usually > 10 mm long, margined |
| 24 | Fruit globose, c. 6 cm diam. Seeds subcircular, margin with double wing. — Siraitia grosvenorii (Swingle) A.M.Lu & Zhi Y.Zhang, cultivated in China, and sold in Malesia for its sweet, medicinal fruit |
| 24' | Fruit larger, globose, ellipsoid or cylindrical. Seeds elliptic in outline, not winged |
| 25 | Fruit globose, short-ellipsoid or pyriform. Seed edge not undulate |
| 25' | Fruit long-cylindrical. Seed edge coarsely undulate |
| 26 | Fruit large, globose, with 6 large seeds 5-8(-10) cm long. Probract sharp, thorn-like |
| 26' | Fruit various, smaller, less than 10 cm long, seeds more than 6 (1 or 2 in Kedrostis). Probract not sharp at apex, or absent |
| 27 | Seeds tumid (barrel-shaped or (sub)fusiform), or pyriform (see Fig. 19b,Fig. 91b) |
| 27' | Seeds either subglobose, or elongate, little or much compressed (ornamented or not) |
| 28 | Fruit c. 2 cm diam., green, later red and white-blotched or -striped, (sub)sessile |
| 28' | Fruit > 2 cm diam., pedicelled |
| 29 | Fruit 5 cm long or more, seeds 1 cm long or more. Flowers large, petals white, long-fimbriate |
| 29' | Fruit shorter or longer than 5 cm, seeds various. Flowers small or large; petals yellow or white, not long-fimbriate |
| 30 | Tendrils several-branched (2- or more-branched). Probract conspicuous. Petals large, longer than 2 cm, yellow |
| 30' | Tendrils unbranched or 2-branched. Probract small or absent. Petals yellow or greenish, smaller, less than 1.5 cm long, or petals white |
| 31 | Fruit brown, operculate |
| 31' | Fruit green or usually with whitish bloom; not operculate |
| 32 | Flowers large, white; petals free, c. 20 mm long. Tendrils unbranched or unequally 2-branched near the base |
| 32' | Flowers medium or small, white (whitish) or yellow; petals either (almost) free, 15 mm long or less, or petals largely fused and flowers large. Tendrils unbranched or 2-branched towards the apex |
| 33 | Flowers large, white, corolla c. 25 mm long, petals fused for c. 2/3. Fruit glabrous, pulp or juice red |
| 33' | Flowers smaller, white or yellow, corolla c. 20 mm long or less, petals free or short-connate at base only. Fruit glabrous or hairy, pulp or juice white or yellow |
| 34 | Fruit globose, c. 5 cm diam. Seeds with 2- or 3-winged margin. Leaf blade with minute blackish appressed glandular hairs |
| 34' | Fruit globose, or ellipsoid or fusiform, small or large. Seeds not winged. Blackish glandular hairs absent |
| 35 | Flowers medium, petals c. 10 mm long, yellow |
| 35' | Flowers small, petals c. 5 mm long or less, white, greenish or yellow |
| 36 | Female flowers or fruit solitary, in non-pedunculate raceme at the end of shoots, or flowers 4-7 in a short raceme. Fruit c. 5 cm long, smooth; seeds few or several, large, c. 9 mm long, subglobose, smooth. — Borneo |
| 36' | Female flowers or fruit on the leaf-bearing node. Fruits various; seeds numerous, smaller, ornamented |
| 37 | Fruit hairy, glabrescent (see Fl. China). — Philippines |
| 37' | Fruit glabrous. — New Guinea |
| 38 | Stigma 3 times parted, finely feather-like. Disc not obvious (absent) |
| 38' | Stigma 3-lobed (papillose). Disc urceolate, largely adnate to the base of the receptacle-tube |
| 39 | Fruit globose, 3-4.5 cm across, hairy. — Borneo |
| 39' | Fruit globose but much smaller, c. 1 cm diam., or fruit ellipsoid or ovoid |
| 40 | Seeds nearly globose, smooth |
| 40' | Seeds elongate, somewhat or much compressed. Petiole mostly long |
| 41 | Petiole short. Flowers creamy-white. Fruits 2-5 cm long. Seeds 5-20 |
| 41' | Petiole long, usually at least as long as half the length of the blade. Flowers yellow. Fruit 1-1.5 cm long. Seeds 1 or 2 |
| 42 | Fruit broad-ellipsoid, 2-5 cm long. Seeds smooth [Thecae plicate.] |
| 42' | Fruit various, when more than 5 cm long then elongate-fusiform. Seeds smooth or scrobiculate (pitted or warted). [Thecae plicate or not plicate.] |
| 43 | Tendrils 2-branched. [Thecae plicate.] — East Java, naturalized |
| 43' | Tendrils unbranched [Thecae not plicate.] |
| 44 | Fruit (sub)sessile, (few-)fascicled; fruiting pedicel to 10 mm long. Corolla yellow. (Male) flowers short pedicelled in (sub)sessile fascicles or clusters |
| 44' | Fruit with short or longer pedicel. Corolla white or yellow. (Male) flowers long-pedicelled or when shorter pedicelled then arranged in (small) pedunculate racemes or fascicles |
| 45 | Seeds thickish, margined, faces pitted or warted. Corolla yellow |
| 45' | Seeds compressed (or globose), faces smooth, glabrous or hairy |
| 46 | Fruit c. 1 cm diam. — West Malesia |
| 46' | Fruit c. 2 cm diam. — New Guinea |
| 47 | Corolla yellow, petals ± notched at apex. Fruits purple-black; seeds hairy |
| 47' | Corolla white, petals not notched. Fruit green, red or purple; seeds smooth or hairy |
| 48 | Seeds narrowly margined. Probract (small, linear) present. Fruiting pedicel short, usually shorter than the fruit |
| 48' | Seeds unmargined. Probract absent. Fruiting pedicel short or long |
| 49 | Stigma 3-parted, parts sessile or short-armed. Disc ring-shaped. Fruits solitary or (few-)fascicled, small, to 1.5 cm long |
| 49' | Stigma parts long-armed, each 2-lobed. Disc 3-parted. Fruit 1.2-2 cm long. — Norfolk Is. (not in Malesia) |
| 50 | Seeds glabrous, sometimes short-winged at one side. Female flowers or male flowers one or few, long-pedicelled, inserted at the node. Fruit globose, or ellipsoid, or fusiform, green or red |
| 50' | Seeds hairy, not winged. Female flowers with long pedicel solitary on the node, co-axillary with male inflorescence. Male flowers in a pedunculate raceme. Fruit (long) fusiform, green |
