Key for Nautilocalyx Linden ex Hanst.

1Corollas red
1'Corollas white, or slightly tinged with pink (tube white with lobes lavender blue in N. cordatus)
2Flower 1 per axil
2'Flowers 2 to several per axil (rarely 1 in N. porphyrotrichus)
3Calyx lobes rounded at apex
3'Calyx lobes acute
4Inflorescences pedunculate; calyx lobes sparsely villous or glabrous outside (cultivated)
4'Inflorescences epedunculate; calyx lobes hirsute or densely villous outside
5Leaf blades subequal in a pair; corolla oblique in calyx
5'Leaf blades unequal in a pair; corolla erect in calyx
6Leaf blades decurrent into petiole
6'Leaf blades not decurrent
7Leaf blades purplish underneath
7'Leaf blades green underneath
8Calyx lobes entire
8'Calyx lobes repand-serrate
9Leaf blades acuminate at apex, cuneate at base
9'Leaf blades obtuse or acute at apex, rounded or subcordate at base
10Calyx lobes with a few teeth; corolla tube 0.8-1.1 cm long
10'Calyx lobes serrate; corolla tube 2.8-5 cm long
11Leaf blades equal in a pair, ovate, below minutely pilose; corolla tube white, 2.8 cm long, lobes white
11'Leaf blades mostly unequal in a pair, oblong-elliptic, below hirsute; corolla tube white, 3.3-5 cm long, lobes lavender