| 1 | Leaf blade foliolate (in T. celebica and T. wawrae leaves sometimes partly or all simple). The 5 species normally with foliolate leaves are insufficiently known in the male flowering state, and hence cannot be keyed out. |
| 1' | Leaf blade simple |
| 2 | Plants stout. Probract concave. |
| 2' | Plants more delicate. Probract ± flat. |
| 3 | Peninsular Malaysia, Singapore, Sumatra, Borneo, Palawan |
| 3' | Moluccas, New Guinea |
| 4 | Peninsular Malaysia, Sumatra, Borneo, Java |
| 4' | Sulawesi, Moluccas |
| 4'' | Lesser Sunda Islands |
| 5 | Plant monoecious. Bracts 1(-2) mm long, caducous. Flowering diurnal. Corolla 20(-30) mm diameter. — Widespread |
| 5' | Plant usually dioecious. Bracts 1 mm long or (much) longer, (late) caducous or persistent. Flowering nocturnal. Corolla 30 mm diam. or more |
| 6 | Younger twig and leaves densely soft-hairy, hairs 2 mm long or more |
| 6' | Younger twig and leaves scabrous, (sparsely) short-hairy or glabrous (glabrescent) |
| 7 | Bracts large, 20-50(-60) mm long. — Borneo, Java, Philippines, Lesser Sunda Islands |
| 7' | Bracts small, c. 1 mm long. — Sabah |
| 8 | Blade base at transition to the petiole with 2 bulgings or auricles with glands beneath (sect. Asterosperma) |
| 8' | Blade base at transition to the petiole without gland-bearing bulgings or auricles |
| 9 | Flowers solitary, axillary to leaves, conspicuously brown-hairy. — Sabah |
| 9' | Flowers in peduncled racemes, minutely grey- or brown-hairy |
| 10 | Inflorescences inserted on older stems, far below the leaves. Bracts narrowly elliptic, entire. — Sabah |
| 10' | Inflorescences axillary to leaves. Bracts elliptic, dentate. — Borneo (Sarawak, Sabah, West, Central, and East Kalimantan) |
| 11 | Leafy stem sharply ridged or winged |
| 11' | Leafy stem striate or grooved |
| 12 | Inflorescences axillary to leaves. Bracts large, broad. — Sabah |
| 12' | Inflorescences pendent, mostly below the leaves. Bracts small, narrow. — Sabah |
| 13 | Plant not from New Guinea. [Specimens with simple unlobed leaves may belong to a species usually with foliolate leaves, 5. T. celebica, or 43. T. wawrae; see lead 1] |
| 13' | Plant from New Guinea (including widespread 30. T. pilosa, 35. T. quinquangulata; see the regional key for New Guinea) |
| 14 | Bracts large, (10-)15 mm long or more |
| 14' | Bracts small, 1-15 mm long |
| 15 | Raceme including bracts finely yellowish soft-hairy; bracts entire, 35-70 mm long. Blade base cuneate-decurrent. Tendrils simple |
| 15' | Raceme including bracts brown-rusty hairy, glabrous or glabrescent. Tendrils branched |
| 16 | Bracts (ob)ovate, margin (sub)entire. — Widespread |
| 16' | Bracts incised |
| 17 | Leaf blade unlobed, margin coarsely dentate, blade glands few, large, 2-3 mm diameter. — Philippines |
| 17' | Leaf blade unlobed or lobed, margin finely remotely denticulate, blade glands smaller |
| 18 | Rachis zigzag. — Borneo, Philippines; peat swamp forest |
| 18' | Rachis straight |
| 19 | Bracts broad, deeply fan-shaped incised. Plant dull blackish on drying. — Borneo |
| 19' | Bracts variously incised, but not deeply fan-shaped incised. Plant green, (reddish) brown or blackish on drying |
| 20 | Younger parts reddish on drying |
| 20' | Younger parts green, brown or blackish on drying |
| 21 | Probract narrowly elliptic or linear, 10-20 by c. 2 mm. Leaf blade finely hairy beneath. — Western Malesia |
| 21' | Probract obovate or narrowly elliptic, 10-15 by 5-8 mm. Leaf blade ± scabrous beneath. — North Sumatra |
| 22 | Bracts (deeply) finely incised. Leaf blade 3-lobed to about halfway deep, greenish on drying. — Philippines |
| 22' | Bracts coarsely incised, i.e. at apex dentate. Leaf blade unlobed or variously lobed, greenish (brown) or brown on drying |
| 23 | Rachis stout, 3-7 mm diameter |
| 23' | Rachis more slender, 1.5-3 mm diameter |
| 24 | Leaf blade unlobed or shallowly (2- or)3-lobed, to 1/3 deep |
| 24' | Leaf blade deeply 3-7-lobed |
| 25 | Blade glands scattered or at base only, 1-2 mm diameter. Peduncle 9-18 cm long. Bracts 40-50 mm long. — East Malesia |
| 25' | Blade glands absent or few near blade base, 1-3 mm diameter. Peduncle 2-6 cm long. Bracts 40-60 mm long. — West Malesia |
| 26 | Leaf blade unlobed. — Sarawak, Philippines |
| 26' | Leaf blade lobed |
| 27 | Leaf blade 3-lobed, to 1/3-2/3 deep (leaves unlobed in forma siberutensis). — Widespread in West Malesia [Sumatra, Peninsular Malaysia, Singapore, Borneo, Java, Sulawesi, Lesser Sunda Islands, and Moluccas] |
| 27' | Leaf blade more deeply 5-lobed |
| 28 | Probract c. 4 by 2 mm, with few glands. — North Sumatra, Peninsular Malaysia |
| 28' | Probract 5-18 by 1-2 mm, glands absent. — Sumatra, Peninsular Malaysia, Singapore, Borneo |
| 29 | Leaf blade unlobed, in outline circular, glabrous. — Sumatra |
| 29' | Leaf blade unlobed or lobed, in outline broadly ovate, glabrous or hairy |
| 30 | Leaf blade finely hairy beneath, at least along the (finer) veins. [Bracts (2-)5-15 mm long.] — Widespread |
| 30' | Leaf blade scabrous-hairy or (sub)glabrous beneath |
| 31 | Leaf blade unlobed, large, (8-)12-23 cm long, when older coriaceous, with recurved margin. [Bracts 5-7 mm long.] — Sumatra, West Java |
| 31' | Leaf blade unlobed and often smaller, or (deeply) lobed |
| 32 | Veins raised beneath. Bracts minute, 1-3 mm long, caducous |
| 32' | Veins not or hardly raised beneath. Bracts larger, persistent |
| 33 | Leaf blades almost adherent to supporting tree trunk, scabrous. — Sabah |
| 33' | Leaf blades free (plant climbing freely), faintly scabrous or glabrous |
| 34 | Leaf blade unlobed or deeply 3(-5)-lobed. Pedicel remnants on rachis short, shorter than the bracts, bracts 6-15 mm long. — Sabah |
| 34' | Leaf blade deeply 5-lobed. Pedicel remnants on rachis about as long as bracts, bracts 7-12 mm long. — Northern Kalimantan, Sarawak, and Sabah. |
| 35 | Leaf blade finely hairy beneath, especially along the smaller veins. Petals (excluding fringes) (narrowly) elliptic or (narrowly) ovate. — Widespread |
| 35' | Leaf blade variously hairy or glabrous beneath. Petals obtriangular (cuneate) |
| 36 | Bracts entire, 10-30 mm long. — Widespread |
| 36' | Bracts dentate (incised), sometimes at very apex only, or bracts much smaller. Eight species endemic to New Guinea (male flowers not known in T. dentifera; see regional key for New Guinea, lead 11 onwards: T. dentifera, T. dieniensis, T. densiflora, T. edulis (3 varieties), T. hastata, T. laeoica (4 forms), T. pulleana, T. schlechteri). |
