| 1 | Flowers and fruits sessile |
| 1' | Flowers and fruits pedicellate |
| 2 | Calyx in bud closed or closed with an apical pore |
| 2' | Calyx open with free sepals in bud |
| 3 | Leaf margins serrate-crenulate |
| 3' | Leaf margins entire |
| 4 | Calyx in bud with an apical pore |
| 4' | Calyx in bud completely closed |
| 5 | Fruit distinctly 4-winged, hypanthium tetragonous, winged or sharply angled |
| 5' | Fruit circular in section to subtetragonous, not winged; hypanthium at most only slightly angled |
| 6 | Calyx and inflorescence rachis glabrous; fruit ovoid, subtetragonous, lightly winged when young |
| 6' | Calyx and inflorescence rachis densely short-pubescent; fruit cylindrical-8-sided, not winged |
| 7 | Leaf laminas 100-190(-228) by 22-42 cm; staminal whorls 8-12; hypanthium velvety pubescent, rounded-cupular; fruit without basal hooks |
| 7' | Leaf laminas 29-62 by 8-24 cm; staminal whorls 5-6; hypanthium pulverulent, tetragonous; fruit with hooks near base on alternate ribs |
| 8 | Staminal whorls 8, 3 innermost staminodal, inner whorl exceeding staminal tube |
| 8' | Staminal whorls 3-7, 1(-2) staminodal, inner whorl not exceeding staminal tube (except in B. calyptrata) |
| 9 | Inflorescence cauline to ramiflorous; calyx and inflorescence rachis densely fulvous- pubescent or sparsely grey puberulous; calyx circumscissile |
| 9' | Inflorescence terminal; calyx and rachis glabrous or slightly pulverulent; calyx opening in 2-5 segments |
| 10 | Inflorescence densely fulvous or grey-green pulverulent; staminal whorls 4-5(-7) |
| 10' | Inflorescence sparsely grey-puberulous; staminal whorls 3. |
| 11 | Inflorescence with flowers grouped at apex; leaf apex mucronate |
| 11' | Inflorescence with flowers spaced along rachis; leaf apex rounded to cuspidate |
| 12 | Primary leaf veins 8-15 pairs; twigs 2-4 mm diam.; staminal tube 1-2 mm high |
| 12' | Primary leaf veins 12-50 pairs; twigs 7-20 mm diam.; staminal tube 4-5 mm high |
| 13 | Fruit with 3-5 seeds (unknown for B. terengganuensis) |
| 13' | Fruit single seeded |
| 14 | Leaf petiole 4-5 mm long |
| 14' | Leaf petiole 10 mm or more long |
| 15 | Leaf margins entire; petioles 1-9 cm long; primary leaf veins 6-9 pairs; inflorescence usually short, 3-12(-26) cm long; fruits large, 9-16 cm diam. |
| 15' | Leaf margins serrate-crenulate; petioles 3-12 cm long; primary leaf veins 11-30 pairs; inflorescence more than 20 cm long; fruits 3-5 cm long |
| 16 | Leaf laminas elliptic; petioles 2 cm or more long; inflorescence 5-12(-26) cm long; fruit 9 cm diam. |
| 16' | Leaf laminas obovate; petioles 1-2 cm long; inflorescence 2-3 cm long; fruit c. 16 cm diam. |
| 17 | Leaf laminas linear-lanceolate |
| 17' | Leaf laminas ovate to elliptic to oblanceolate |
| 18 | Leaf laminas elliptic, chartaceous; petioles less than 6 cm long, slightly winged; primary leaf veins 14 pairs or less; ovary 4-locular |
| 18' | Leaf laminas ovate to oblanceolate, coriaceous; petioles 4 cm or more long, not winged; primary leaf veins 14-30 pairs; ovary 3-locular |
| 19 | Hypanthium glabrous |
| 19' | Hypanthium pubescent or pulverulent |
| 20 | Leaf margins entire to slightly serrate-crenulate; inflorescence an erect ramiflorous cluster of spikes, 0.5-2.5 cm long |
| 20' | Leaf margins serrate-crenulate; inflorescence a pendulous raceme or spike |
| 21 | Ovary 2-(3-4)-locular; stamens in 3 whorls |
| 21' | Ovary 4-locular; stamens in 4-5 whorls |
| 22 | Fruit dull, teretish, at most with 4 ribs, mostly with convex sides, 5.5-9 by 2-4 cm; leaf laminas 10-45 by 4-10 cm, chartaceous with flattish margin |
| 22' | Fruit rather smooth, shiny, conspicuously tetragonous with clear angles and flat or depressed sides, 6-10.5 by 2.5-7 cm; leaf laminas 11-22 by 3-8 cm, coriaceous, with recurved margin |
| 23 | Ovary 2-(3-4)-locular; stamens in 3 whorls |
| 23' | Ovary 3-4-locular; stamens in 4-7 whorls |
| 24 | Leaf laminas 26-28.5 by 7-7.5 cm |
| 24' | Leaf laminas 6-18 by 2-13 cm |
| 25 | Leaf laminas elliptic or obovate-oblong, broadest below middle, 6-16 by 2-8 cm, glabrous beneath; petiole 4-15 mm |
| 25' | Leaf laminas obovate-spathulate, broadest above middle, 14-18 by 6-13 cm, densely hirsute on venation beneath; petiole 0-8 mm long |
| 26 | Hypanthium tetragonous, angled, conspicuously winged on corners |
| 26' | Hypanthium teretish and grooved or tetragonous, terete or angled but without wings or grooves |
| 27 | Primary leaf veins 16-30 pairs; petioles 0.3-2 cm long; stamens in 5-6 whorls; fruit tetragonous or trigonous, 5-7 cm long |
| 27' | Primary leaf veins 7-10 pairs; petioles 0.5-5 cm long; stamens in 4-5 whorls; fruit usually ovoid, rarely tetragonous, 10-12 cm long |
| 28 | Hypanthium tetragonous, terete or angled, but without grooves, pubescent but not ferrugineous; inflorescence terminal; primary veins 15-30 |
| 28' | Hypanthium teretish to tetragonous, with 4 distinct grooves, ferrugineous pubescent; inflorescence ramiflorous; primary veins 8-18 |
| 29 | Calyx in bud closed or with a small apical pore |
| 29' | Calyx open in bud with free sepals |
| 30 | Leaf margins serrate-crenulate throughout |
| 30' | Leaf margins entire (to slightly, sometimes partly crenulate) |
| 31 | Primary leaf veins 32-95; leaf laminas linear-lanceolate or obovate-lanceolate |
| 31' | Primary leaf veins 8-45; leaf laminas usually oblong to oblong-lanceolate to obovate-lanceolate or linear lanceolate (except B. boridiensis and B. pinnifolia where narrowly lanceolate) |
| 32 | Primary leaf veins 32-65 pairs; inflorescence pendulous; flowers pink or red |
| 32' | Primary leaf veins 70-95 pairs; inflorescence more or less erect; flowers white |
| 33 | Leaf laminas narrowly lanceolate; primary veins 18-38 |
| 33' | Leaf laminas elliptic, narrowly obovate, oblong-obovate, oblong to oblong-lanceolate; primary veins 8-45 |
| 34 | Monocaulous tree; leaf laminas tapering from mid point; primary veins 18-38 |
| 34' | Branched tree; leaf laminas tapering from 4/5 to 5/6 of length; primary veins 21- 26 |
| 35 | Staminal whorls 2-3 |
| 35' | Staminal whorls 4-8 to numerous |
| 36 | Primary leaf veins 38-45 pairs; leaf laminas 80-90 by 19-22 cm |
| 36' | Primary leaf veins 8-28 pairs; leaf laminas 3-52 by 1.5-9 cm |
| 37 | Primary leaf veins 8-10; ovary 2-locular, not winged; fruit c. 2.5 by 0.5 cm |
| 37' | Primary leaf veins 15-28; ovary 3-4-locular, 4-winged; fruit 4-6 by 1-2.5 cm |
| 38 | Mature fruit conoid with 8 wings at emarginate base; hypanthium with 8-winged appendages |
| 38' | Mature fruit tri- or tetragonous or oblong-cylindric, not winged or only slightly 4-winged when young (fruit unknown for B. serenae); hypanthium without appendages |
| 39 | Leaf margin distinctly revolute; staminal whorls 4; fruit distinctly pedicelled |
| 39' | Leaf margin flat; staminal whorls 5 or more (except 4 in B. monticola); fruit often sessile except in B. clemensii |
| 40 | Style much shorter than stamens; pedicel articulate |
| 40' | Style equalling or exceeding stamens; pedicels not articulate |
| 41 | Calyx not circumscissile; fruit ovoid, subtetragonous |
| 41' | Calyx circumscissile, fruit ellipsoid, cylindric or rounded-ovoid to ovoid |
| 42 | Small branching tree, 6-15 m tall; flowers subsessile, pedicels 1-5 mm long; hypanthium tetragonous, pulverulent |
| 42' | Trees, monocaulous (not branching), to 4 m tall, or leptocaulous (few branches), to 20 m tall; pedicels 1-2 or 8-15 mm long; hypanthium cone-shaped, glabrous |
| 43 | Monocaulous tree; leaf laminas 65-85 by 13-19 cm; primary veins 25-35, montane |
| 43' | Leptocaulous (branching) tree; leaf laminas 16-33 by 5-12 cm; primary veins 12-17, lowland |
| 44 | Calyx in bud with an apical pore |
| 44' | Calyx in bud without an apical pore |
| 45 | Fruit ellipsoid; leaf blade margin flat, apex acuminate; staminal whorls 5-8 (introduced in New Guinea for edible seeds) |
| 45' | Fruit (sub)tetragonous; leaf blade margin (slightly) revolute, apex usually acuminate (Borneo) or cuspidate to caudate (New Guinea); staminal whorls 4 (Borneo) or 8-10 (New Guinea) |
| 46 | Staminal whorls 4; fruit oblong, tetragonous, 13-14 by 5-5.5 cm; inflorescence rachis yellowish puberulous |
| 46' | Staminal whorls 8-10; fruit subtetragonous, 4-7.5 by 1.5-3.5 cm; inflorescence rachis pulverulent to glabrous |
| 47 | Inflorescence erect |
| 47' | Inflorescence pendulous |
| 48 | Fruit markedly tetragonous at base, ovate, 8.5-11 cm long; petioles 0-5 mm long; venation cladodromous; sepals 3-4 by 2-3 cm |
| 48' | Fruit not tetragonous at base, ovate-oblong to 4 cm long; petioles 6-12 mm long; venation brochidodromous; sepals 1.2-1.4 by 0.9-1.1 cm |
| 49 | Leaves subsessile, petioles 0-7 mm |
| 49' | Leaves distinctly petiolate; petioles 0.5-8 cm long |
| 50 | Inflorescence infrafoliar; primary veins 16-27 pairs; hypanthium glabrous; leaf laminas (14.5-)27-41.5 by (3.5-)5-9.5 cm |
| 50' | Inflorescence terminal; primary leaf veins 9-11 pairs; hypanthium puberulous; leaf laminas 15-27.5 by 3.5-6.5 cm |
| 51 | Inflorescence rachis 3-7 cm long |
| 51' | Inflorescence rachis 10-80 cm or more long |
| 52 | Hypanthium glabrous |
| 52' | Hypanthium pubescent |
| 53 | Leaf margins flat, primary veins 7-14 pairs |
| 53' | Leaf margins distinctly revolute; primary veins 14-16 pairs |
| 54 | Hypanthium terete to slightly tetragonous; inflorescence axillary, terminal or rami- florous |
| 54' | Hypanthium tetragonous, trigonous or angled (terete in B. confusa, then primary veins 17-28 pairs); inflorescence cauliflorous, ramiflorous or axillary |
| 55 | Leaf margins flat; primary veins 11-20 pairs |
| 55' | Leaf margins revolute; primary veins 11-13 pairs |
| 56 | Inflorescence axillary or ramiflorous; petals creamy yellow |
| 56' | Inflorescence terminal; petals red |
| 57 | Primary leaf veins 7-14 pairs |
| 57' | Primary leaf veins 17-28 pairs |
| 58 | Leaf laminas 16-29 cm broad, widest at ⅔ of length, flowers borne on 1 mm long bosses and pedicels 8-10 mm long |
| 58' | Leaf laminas 6-17 cm broad, widest at mid point; pedicels 6-16 mm |
| 59 | Leaves sessile or subsessile |
| 59' | Leaves distinctly petiolate (most over 5 mm) |
| 60 | Leaf margins entire; adventitious roots on stem; inflorescence erect when young becoming pendulous only in fruit |
| 60' | Leaf margins serrate-crenulate; without adventitious roots on stem; inflorescence pendulous |
| 61 | Inflorescence and hypanthium ferrugineous pubescent; fruit usually fusiform |
| 61' | Inflorescence and hypanthium glabrous; fruit ovoid with 4 knobs at base |
| 62 | Primary leaf veins 35-45 pairs; petioles 9-14 cm; buds c. 1.5 cm diam. |
| 62' | Primary leaf veins 7-32 pairs; petioles 0.1-11 cm; buds 0.5-1 cm diam. |
| 63 | Ovary 2-locular; primary leaf veins 7-12 pairs; fruit acutely angled, slightly winged when young |
| 63' | Ovary 3-4-locular; primary leaf veins 10-32 pairs; fruit ovoid or spindle-shaped, tetragonous, obovate, not winged except in B. macrocarpa (fruit unknown for B. havilandii) |
| 64 | Inflorescence erect, 4.5-7 cm long |
| 64' | Inflorescence pendulous, exceeding 20 cm long |
| 65 | Leaf laminas 19-70 by 6-18 cm; primary veins 16-32 pairs; petals 17.5-30 by 7.5-16 mm |
| 65' | Leaf laminas 9.5-26 by 2.5-9 cm; primary veins 11-18 pairs; petals 12-20 by 6-11 mm |
| 66 | Inflorescence and hypanthium pulverulent |
| 66' | Inflorescence and hypanthium glabrous |
| 67 | Leaf lamina slightly decurrent; inflorescence, rachis and hypanthium glabrous |
| 67' | Leaf lamina not decurrent; inflorescence rachis puberulous; hypanthium ferrugineous |
