| 1 | Pistil 2(-4)-merous. (Exceptionally a few flowers with a 1-merous ovary) |
| 1' | Pistil 1-merous |
| 2 | Fruit wall coriaceous or eggshell-like, rarely more than l(-7) mm thick |
| 2' | Fruit wall hard, corky, 3-6 mm thick, the saccate base and the carina of the fruit solid |
| 3 | Fruits warty, the warts without a distinct apical appendage. (In a few cases this character may be difficult. Try both ways) |
| 3' | Fruits not warty, the appendages usually distinctly divided into a broader or thicker basal and a narrower apical part |
| 4 | At least the upper half of the fruit appendages densely puberulous |
| 4' | Fruits glabrous |
| 5 | Leaf axes densely tomentellous, sometimes glabrescent. Leaflets hairy all over above, soon glabrescent, the midrib sometimes excepted, tomentose on midrib and nerves beneath, densely sericeous in between. Calyx 3 mm high |
| 5' | Leaf axes sparsely puberulous to glabrous. Leaflets glabrous above, sparsely sericeous all over beneath, sometimes glabrescent. Calyx up to 1.75 mm high 15. N. melanomiscum 6a. Leaflets mostly widest at about ⅓ above the base; reticulation on upper side dense. Fruits aculeate |
| 5'' | Leaflets widest at or sometimes slightly below the middle; reticulation on upper side lax. Fruits tuberculate |
| 6 | Leaflets obtuse to acute; veins reticulate; domatia usually present. Burma, Thailand, Indochina |
| 6' | Leaflets tapering into a long and broad acumen; veins especially on the lower side rather distinctly scalariform; domatia absent. Borneo |
| 7 | Leaves up to 7-jugate. Leaflets usually almost parallel-sided, abruptly rounded at the base, flat when dried. Fruits coarsely warty, the warts ± arranged into longitudinal rows. Malay Peninsula, Sumatra, Java |
| 7' | Leaves 2- or 3-jugate. Leaflets with strongly curved sides, tapering to the cuneate base, often curled or rolled up when dried. Fruits densely knobby like a small Pan-danus fruit head, the knobs not confluent. Borneo An unusual form of |
| 8 | Fruit appendages distinctly puberulous all over |
| 8' | Fruits (sub)glabrous or exceptionally with a hair tuft on the tops of the appendages |
| 9 | Petiolules above grooved. Leaflets symmetrical |
| 9' | Petiolules above not grooved. Leaflets slightly falcate. |
| 10 | Leaflets beneath glabrous or nearly so |
| 10' | Leaflets beneath densely tomentose on and along midrib and nerves, distinctly to moderately densely sericeous in between |
| 11 | Veins and veinlets densely reticulate, above not very conspicuous, beneath inconspicuous. Leaflets drying brown |
| 11' | Veins and veinlets on both sides of the leaflets conspicuously ± laxly reticulate. Leaflets drying green |
| 12 | Twigs and leaf axes (sub)glabrous. Fruit appendages less than 10 mm long. Vietnam, Thailand, Malay Peninsula |
| 12' | Twigs and leaf axes tomentellous or puberulous, early glabrescent. Fruit appendages c. 15 mm long. Borneo |
| 13 | Domatia usually present. Sepals 2-3 mm long. Fruit appendages filiform, c. 7 mm long, sparsely puberulous |
| 13' | Domatia absent. Sepals 1-1.8 mm long. Fruit appendages ligulate to strap-shaped, up to 6(-9) mm long, ± densely puberulous |
| 14 | Domatia present |
| 14' | Domatia absent |
| 15 | Reticulation on the upper side of the leaflets dense |
| 15' | Reticulation on the upper side of the leaflets lax |
| 16 | Fruits up to 2.5 by 1.5 cm, wall up to 1 mm thick, appendages up to 10 mm long. Venation reticulate |
| 16' | Fruits up to 6 by 3.5 cm, wall up to 2.5 mm thick, appendages usually more than 10(-20) mm. Venation often tending to scalariform |
| 17 | Leaves typically up to 6-jugate. Leaflets up to 5.5 times as long as wide, distinctly long- and slender-acuminate, parallel-sided. Fruit appendages sparse, 2-3(-8) mm long, upper part ligulate |
| 17' | Leaves 1- or 2-jugate. Leaflets c. 2-3.5 times as long as wide, short- and broad-cicuminate, sides curved. Fruit appendages dense, 8-10 mm long, upper part filiform |
| 18 | Inflorescences usually truly terminal, not ending in a vegetative bud, infructescenc-es thus also terminal. Fruit appendages ± hair-like or sometimes ± tongue-shaped. Leaflets when dried mostly flat |
| 18' | Inflorescences axillary and pseudoterminal, the latter ending in a vegetative bud, infructescences thus lateral. Fruits mostly densely spiny, sometimes knobby. Leaflets when dried often curled or rolled up |
| 19 | Leaflets pergamentaceous, apex not mucronate, midrib raised above, intercalated veins well developed, venation reticulate. Fruits up to 3 by 2.25 cm, appendages sparse and short, up to 7.5 mm long |
| 19' | Leaflets coriaceous, apex usually mucronate, midrib usually sunken above, interca-lated veins mostly inconspicuous, venation tending to scalariform. Fruits up to 6 by 3.5 cm, appendages dense, up to 2 cm long |
| 20 | Fruit appendages mostly filiform. Leaflets mostly flat when dried |
| 20' | Fruit with long spines. Leaflets when dried often curled or rolled up |
| 21 | Leaflets nearly always hairy below, at least on the midrib |
| 21' | Leaflets below glabrous or at most with a few minute hairs along the midrib. 24 23a. Twigs and leaves usually densely though sometimes minutely hairy, rarely glabrous. Inflorescences axillary and/or pseudoterminal |
| 21'' | Twigs and leaves sparsely hairy to glabrous. Inflorescences mostly truly terminal 10. N. lappaceum 24a. Apical part of the fruit appendages thread- or hair-like, up to 15 mm long. Leaflets rather abruptly ± caudate-acuminate |
| 21''' | Apical part of the fruit appendages nipple-like, 1-2 mm long. Leaflets hardly short- and broad-acuminate |
| 22 | Reticulations of the leaflets minute, not elongated parallel to the nerves. Apical part of the fruit appendages up to 10 mm long, slightly hairy. |
| 22' | Reticulations of the leaflets lax, elongated parallel to the nerves. Apical part of the fruit appendages up to 15 mm long, glabrous |
