Shrubs to shrubby trees 2-7 m tall, new growth yellowish brown puberulent and with a waxy scurf, soon glabrate; stems usually many-branched.
Leaves with a strong, pungent anise odor when crushed, opposite, thin, coriaceous, elliptic-obovate, elliptic, or broadly oblong-elliptic, flat to sometimes strongly revolute, (4.5-)6-17 cm long, often less than 12 cm long, 2.5-8 cm wide, primary lateral veins 7-15 pairs, ascending, connected by a weakly arched vein 1-5(-9) mm from margin, higher order venation forming a prominent reticulate pattern, both surfaces glabrate except midrib on lower surface usually with a few scattered hairs, apex rounded, ± emarginate, base
cuneate to subtruncate, petioles 6-45 mm long.
Flowers functionally unisexual or perfect (usually with both staminate and perfect flowers on a single plant), usually 3-5(7) in short, glabrate to sparsely puberulent, axillary cymes usually less than 2 cm long, peduncles 3-4 mm long, pedicels ca. 3 mm long, bracteoles minute, deltate, puberulent or glabrate; sepals deltate-ovate, 1.8-2.2 mm wide, minutely ciliate, otherwise glabrous; petals deltate, 4.5-6 mm long, glabrous; nectary disk glabrous; ovary ca. 1 mm long, glabrous; style slender, ca. 2 mm long, glabrous.
Capsules depressed-cuboid to depressed-cuboid-globose, ca. 9 mm long, 10-14 mm wide, unlobed or weakly lobed, exocarp and endocarp glabrous.
Seeds 1(2) per carpel, 5-6 mm long.
M. oahuensis is differentiated from M. anisata only in its more common tree habit with many-branched stems, and in its tendency toward elliptic-obovate leaves less than 12 cm long. The 2 species probably should be combined; however, the variation pattern should first be carefully analyzed.