[2] M. pleiogynus is an evergreen tree growing up to 43 m (141 ft) tall, with a trunk diameter of up to 70 cm (28 in).

There are 2-4 large, dark brown nectaries at the base of each leaf on the upper surface.

M. pleiogynus is dioecious and the inflorescences are racemes, produced singly or less commonly in a pair.

Male plants produce inflorescences up to 17 cm (6.7 in) long, with dark coloured flowers measuring 1.8–3.5 mm (0.071–0.138 in) in diameter and composed of 3-4 pointed sepals surrounding a cluster of 15-50 stamens.

Female plants produce inflorescences up to 7.8 cm (3.1 in) long, each flower measuring 3.5–7 mm (0.14–0.28 in) in diameter and bearing 4-6 sepals and several plumose stigmas.