| 1 | Tendrils distally 2-branched. Inflorescences paniculate; bracts usually minute, 1-2 mm long. Flowers small, petals less than 5 mm long (6-8 mm long in Alsomitra) whitish or pale off-yellow, or purple-red in Bayabusua, never yellow. Stamens 3 (Alsomitra, Bayabusua), or 5 evenly spaced; filaments inserted on or near the disc (if present). Pollen small, striate. (Styles 3. Fruit a capsule (except Gynostemma)). |
| 1' | Tendrils simple or branched at or below the middle (except Baijiania and Siraitia with tendrils distally 2-branched). Flowers solitary, or fascicled, or in racemes, or in panicles but then petals usually larger; bracts small or large. Flowers small or large, petals white, off-yellow or bright yellow. Stamens 3, or 5 but then 4 in two pairs and 1 solitary; filaments inserted on the receptacle-tube. Pollen generally larger, generally not striate. (Style 1. Fruit usually a berry). |
| 2 | Large climber 15-30 m long. Stamens 3, anthers 3 or 5 |
| 2' | Small or large climber 1-15 m long. Stamens 5, anthers 1 mm long or less, all one-thecous |
| 3 | Petals valvate. Anthers 3-4 mm long, 2 two-thecous, 1 one-thecous. Perianth creamy |
| 3' | Petals imbricate. Anthers c. 2 mm long, white, two filaments with two anthers, one filament with one anther, all anthers one-thecous. Perianth red |
| 4 | Leaf blade simple, margin entire; petiole scar raised when dry. Inflorescences on the older wood. Perianth fleshy, c. 6 mm diameter |
| 4' | Leaf blade often foliolate, margin entire or serrate; petiole scar not raised when dry. Inflorescences terminal or among the leaves. Perianth membranous, small but various of size |
| 5 | Filaments united into a solid column |
| 5' | Filaments free (or united into a hollow column in Neoalsomitra hederifolia) |
| 6 | Blade margin entire |
| 6' | Blade margin serrate-dentate |
| 7 | Petals or corolla (petals free or partly united) 8 mm long or more (open corolla more than 15 mm diam.) |
| 7' | Petals or corolla less than 8(-10) mm long |
| 8 | Petals yellow or greenish, or in Momordica, partly, near-white with dark blotch at base |
| 8' | Petals white, sometimes green veined, or pink, rarely with some yellow |
| 9 | Flowers solitary, with conspicuous bract on flower stalk |
| 9' | Flowers either solitary, or in clusters, racemes, or panicles, without conspicuous bract on flower stalk (probract may be present or absent) |
| 10 | Corolla pale greenish yellow. Filaments united. — [Flowers in short-stalked clusters arranged in pseudo-racemes. Vigorous climber. Usually cultivated] |
| 10' | Corolla light or dark yellow. Filaments free (but anthers may be connate). — [Habit of plant and disposition of flowers various] |
| 11 | Flower solitary or in (sub)sessile clusters |
| 11' | Flowers in racemes or panicles |
| 12 | Probract conspicuous. Petals free |
| 12' | probract absent |
| 13 | Sepals larger, ± recurved. Leaf blade palmately veined or lobed |
| 13' | Sepals minute, patent or recurved. Leaf blade ± pinnately lobed |
| 14 | Tendrils unbranched. Flowers in sessile clusters; corolla c. 2 cm long or less, petals connate for lower 1/3 or less |
| 14' | Tendrils branched. Flowers solitary, corolla larger, petals connate into a tube for c. halfway |
| 15 | Tendrils (2-)3-more-branched at or below the middle. Probract present |
| 15' | Tendrils unbranched or apically 2-branched. Probract absent or present |
| 16 | Receptacle and vegetative parts (especially leaves below) densely set with appressed blackish glandular hairs. Thecae conduplicate (hooked) |
| 16' | Blackish glandular hairs absent. Thecae straight, curved, or convolute, (not hooked) |
| 17 | Stamens 3, or 5, when 5 then four in two pairs, one single. Petals with basal scale |
| 17' | Stamens 3. Petals without basal scale |
| 18 | Flowers in a panicle. — Borneo |
| 18' | Flowers in a pedunculate raceme. — New Guinea |
| 19 | Receptacle-tube short, cup-shaped. Petals largely fused. Filaments fused or tightly coherent |
| 19' | Receptacle-tube elongate. Petals free. Filaments free (anthers coherent) |
| 20 | Apex of petiole with two glands at the transition to the blade |
| 20' | Apex of petiole without glands |
| 21 | Stout climber. Probract thorn-like, triangular, coriaceous, with sharp apex. Petals long fimbriate |
| 21' | Plant of medium or small stature. Probract not thorn-like or absent |
| 22 | Petals not fimbriate |
| 22' | Petals long-fimbriate |
| 23 | Anthers forming a closed continuous ring. — Introduced |
| 23' | Anthers not forming a closed ring |
| 24 | Sepals twice as long as petals |
| 24' | Sepals (as long as or) shorter than petals |
| 25 | Flowers axillary to large bracts |
| 25' | Bracts (minute or) absent |
| 26 | Flowers with short pedicels arranged in an elongate spike-like raceme. Petals yellow. Filaments nodding at apex |
| 26' | Pedicels long or short; flowers in fascicles, or (sub)paniculate, or in pedunculate short racemes. Petals white or yellow. Filaments straight |
| 27 | Anthers (thecae) plicate, contorted, or strongly hooked |
| 27' | Anthers (thecae) straight or ± curved, not plicate |
| 28 | Plant glabrous or scabrous. Filaments distinct; connective not produced |
| 28' | Plant hairy. Leaf blade unlobed or lobed. Filaments short; connective produced |
| 29 | Leaf blade unlobed. Flowers in peduncled raceme. — New Guinea |
| 29' | Leaf blade mostly deeply palmately lobed |
| 30 | Flowers fasciculate in leaf axils |
| 30' | Flowers arranged in loose panicles. — East Java, naturalized |
| 31 | Thecae 2-plicate. Petals (corolla) yellow |
| 31' | Thecae hooked. Petals white |
| 32 | Plant usually glabrous. Leaf blade subcoriaceous, with short petiole |
| 32' | Plant glabrous or hairy. Leaf blade membranous; petiole long (occasionally short in Scopellaria) |
| 33 | Plant coarsely rough-hairy. Flowers subsessile or short-pedicelled (pedicel 2-10 mm long), fascicled at the nodes |
| 33' | Plant glabrous or finely rough or soft-hairy. Flowers either long-pedicelled (pedicel more than 10 mm long) or in a pedunculate raceme |
| 34 | Flowers in a pedunculate raceme. Stamens 3, inserted in or near the throat of the receptacle-tube; anthers two 2-thecous, one 1-thecous |
| 34' | Flowers solitary or (few-)fascicled, directly inserted at the node, usually co-axillary with a female flower, or in a (short) pedunculate raceme or fascicle. Stamens 3; all anthers 2-thecous |
| 35 | Petals (creamy-)white, apex obtuse |
| 35' | Petals yellow, apex notched |
| 36 | Flowers 1 or few, each directly inserted on the node. Stamens inserted near the throat of the receptacle-tube; filaments short, as long as or shorter than the anther, thecae straight. Probract absent |
| 36' | Flowers in a pedunculate raceme or fascicle. Filaments (usually) longer than anthers, thecae straight or curved |
| 37 | Petals white, imbricate or valvate. Stamens inserted halfway or in the lower half in the receptacle-tube, (largely) included. Probract (small, linear) present |
| 37' | Petals yellow, imbricate. Stamens inserted in the throat of receptacle-tube, (largely) exserted. Probract absent |
| 38 | Flowers mostly in a pedunculate raceme. Stamens mostly inserted at (or towards) base of hypanthium-tube; filament longer than anther (shorter in Pilogyne viridifolia) |
| 38' | Flowers in a (sub)sessile fascicle. Stamens inserted about halfway the tube; filament about as long as anther. — Norfolk Is., not in Malesia |
| 39 | Pedicels crowded. Disc free. — SE Asia & West Malesia |
| 39' | Pedicels spaced. Disc urceolate, adnate to base of receptacle-tube. — New Guinea |
