KEY TO THE SPECIES

1	Corolla tube > 7 mm long 2
1'	Corolla tube ≤ 7 mm long 7
2	Inflorescence brown pubescent; calyx lobes brown pubescent 3
2'	Inflorescence glabrous or white puberulent; calyx lobes normally glabrous 6
3	Inflorescence axis longer than the subtending petiole; leaves dull ochre beneath when dry Willughbeia anomala
3'	Inflorescence axis shorter or as long as the subtending petiole; leaves not dull ochre beneath when dry 4
4	Leaves with 1 or 2 intercalcated veins parallel to the secondary veins; stamens inserted in middle of tube Willughbeia oblonga
4'	Leaves with obscure or scalariform tertiary venation; stamens inserted below middle of tube 5
5	Corolla tube 28-30 mm long Willughbeia lunduensis
5'	Corolla tube 7.5-15 mm long Willughbeia tenuiflora
6	Leaves glaucous beneath; corolla tube > 9 mm long, lobes > 12 mm long Willughbeia grandiflora
6'	Leaves not glaucous beneath; corolla tube < 9 mm long, lobes < 12 mm long Willughbeia coriacea
7	Inflorescence brown puberulent 8
7'	Inflorescence glabrous or sparsely white puberulent 9
8	Corolla tube ≤ 3 mm long. — Java Willughbeia javanica
8'	Corolla tube > 3 mm long. — Borneo Willughbeia sarawacensis
9	Inflorescence fasciculate and dense, peduncle shorter than subtending petiole 10
9'	Inflorescence lax, peduncle longer than subtending petiole 13
10	Corolla tube inflated and much wider than head in bud Willughbeia angustifolia
10'	Corolla tube inflated only around anthers, not noticeably wider than head in bud 11
11	Leaves with distinct intercalcated veins between the secondary veins Willughbeia edulis
11'	Leaves with indistinct venation or with veins perpendicular to secondary veins and no intercalcated veins 12
12	Leaves thickly coriaceous, tertiary venation clearly visible perpendicular to and connected between secondary veins; calyx lobes < 1 times as long as wide Willughbeia gigantea
12'	Leaves papery to coriaceous, tertiary venation faint or obscure; calyx lobes > 1 times as long as wide Willughbeia coriacea
13	Tertiary leaf venation largely obscure; leaves glaucous beneath; corolla lobes 3-3.7 mm long Willughbeia ovatifolia
13'	Tertiary leaf venation clearly visible; leaves not glaucous beneath; corolla lobes 1.4-2.8 mm long 14
14	Secondary veins in leaf almost straight with 1-3 intercalcated veins between; leaves dull above and beneath Willughbeia flavescens
14'	Secondary veins in leaf strongly ascending or, if not, then without intercalcated veins and leaves shiny above 15
15	18-30 flowers per inflorescence; leaves dull above, 1.4-2.8 times as long as wide Willughbeia beccariana
15'	8-15 flowers per inflorescence; leaves shiny above, 2.3-3.8 times as long as wide Willughbeia lanceolata