KEY TO THE SPECIES

1Stamens inserted very clearly around the middle or in lower half of corolla tube, ≤ 0.6 of corolla tube length
1'Stamens inserted in upper half of corolla tube, > 0.6 of corolla tube length
2Sepals acute, rarely obtuse but never rounded
2'Sepals rounded
3Inflorescence robust, glabrous to densely pubescent; branchlets glabrous to densely pubescent, terete to very weakly angled. — Peninsular Malaysia
3'Inflorescence delicate, glabrous; branchlets glabrous, weakly angled to strongly winged. — Borneo
4Corolla tube ≤ 20 mm long
4'Corolla tube > 20 mm long
5Branchlets sparsely to densely puberulent, glabrescent when older; petiole sparsely to densely pubescent; sepals densely puberulent
5'Branchlets glabrous; petiole glabrous; sepals glabrous to sparsely puberulent
6Secondary veins 24-32 pairs; corolla lobes < 7 times as long as wide
6'Secondary veins 16-19 pairs; corolla lobes > 8 times as long as wide
7Inflorescence lax with clear internodes, sparsely to densely puberulent; pedicels 2.1-5 mm long
7'Inflorescence with flowers clustered along short or elongated branches, glabrous or puberulent only in upper parts; pedicels 1-2 mm long
8Petiole 4-7 mm long; pedicels 2.1-3.5 mm long; corolla throat pubescent, corolla lobes 9.5-12.3 mm long; disk pubescent; ovary densely pubescent
8'Petiole 1-2 mm long; pedicels 4.5-5 mm long; corolla throat glabrous, corolla lobes 11.5-15 mm long; disk glabrous; ovary glabrous
9Leaf apex caudate, secondary veins clearly discernable from tertiary venation, curved ascending; corolla white, lobes 1-1.5 mm wide
9'Leaf apex short acuminate, secondary veins not clearly discernable from tertiary venation, straight; corolla red, lobes 2.2-2.3 mm wide
10Leaves sessile
10'Leaves petiolate
11Corolla white and tinged pink or pink with a red eye; anther apex < 2 mm from corolla throat
11'Corolla completely white or white with a yellow eye, rarely pinkish white; anther apex > 2 mm from corolla throat
12Disk pubescent; inflorescence lax with distinct internodes
12'Disk glabrous; inflorescence variable
13Petioles delicate, 6-17 mm long, usually around 15% of total leaf length; inflorescence axes < 1 mm wide
13'Petioles robust, 3-12.5 mm long, less than 15% of total leaf length; inflorescence axes > 1 mm wide or rarely less but then corollas not white with a red eye
14Anther apex 5.2-5.8 mm from corolla throat; inflorescence > 10 cm long, densely puberulent
14'Anther apex 0.1-5 mm from corolla throat; inflorescence length variable but mostly < 10 cm long, puberulent or not
15Inflorescence with bracts as large as the sepals and flowers clustered at inflorescence branch ends; sepals mostly acute, more rarely obtuse; fruit without a spur or angle
15'Inflorescence with bracts somewhat obscure or smaller than sepals, if as large as sepals then flowers not clustered at inflorescence branch ends; sepals obtuse to rounded; fruit with a spur or angle on one side
16Ovaries glabrous or with just a few isolated hairs
16'Ovaries clearly pubescent
17Leaves with long caudate apex; secondary veins at 40-60° from midrib. — Borneo
17'Leaves acuminate; secondary veins at (45-)60-75° from midrib. — Not in Borneo
18Stamen bulge slightly below top of corolla tube; flowers white or pinkish but not white with a strongly contrasted pink or red ‘eye’. — Southern Thailand, Peninsular Malaysia
18'Stamen bulge at top of corolla tube; flowers white with a strongly contrasted pink or red ‘eye’. — Philippines, Eastern Malesia, Western Pacific Islands
19Inflorescence robust and lax with distinct internodes all through inflorescence
19'Inflorescence robust or delicate with flowers congested, if lax then at least with ultimate branches congested
20Inflorescence without elongated branches; corolla pale to dark pink or white with a red or pink ‘eye’
20'Inflorescence with elongated branches but with the flowers congested along these; corolla white or white with a yellow ‘eye’, very rarely with a pink tinge but then only ever one flower on an inflorescence branch open at a time
21Branchlets pubescent; native in Burma but widely cultivated
21'Branchlets glabrous; wild
22Peduncle to 1 cm long; fruit with a large deltoid or very slightly hooked projection on one side. — Philippines, Eastern Malesia, Western Pacific Islands
22'Peduncle mostly > 1 cm long, very rarely under 1 cm; fruit with only a slight angle on one side. — Peninsular Malaysia
23Secondary veins at (55-)60-80° from midrib; anther apex 2.4-5 mm from corolla throat
23'Secondary veins at 40-60° from midrib; anther apex 1.1-2 mm from corolla throat