Melicope saint-johnii, a member of the Rutaceae (rue) family, is a slender tree 3 to 6 m (10 to 20 ft) tall. Opposite leaves occasionally occur in threes on young lateral branches. The leaves, 6 to 16 cm (2.4 to 6.3 in) long and 3 to 8.5 cm (1.2 to 3.3 in) wide, are narrowly to broadly elliptic, sometimes elliptic egg-shaped or rarely lance-shaped. Three to 11 flowers are arranged on an flowering stalk 9 to 22 mm (0.4 to 0.9 in) long. The flowers are usually functionally unisexual, with staminate (male) and pistillate (female) flowers. The staminate flowers have broadly egg-shaped sepals which are hairless to sparsely covered with hair. The triangular petals, 6 to 8 mm (0.2 to 0.3 in) long, are densely covered with hair on the exterior. The pistillate flowers are similar in hairiness to staminate flowers but are slightly smaller in size. The dry fruit, 7 to 12 mm (0.3 to 0.5 in) long, splits at maturity. The exocarp (outermost layer of the fruit wall) is hairless, whereas the endocarp (innermost layer) is hairy.