Tree to 20 m high; trunk with d.b.h. to 1 meter; outer bark pale-dark brown to grayish, smooth; young branches drying black, glabrous; old branches ash-grey to pale brown, glabrous. Petioles (2-)5-10(-14) mm long, 1-2 mm in diameter, glabrous, leaf lamina inserted on side, very narrowly grooved adaxially. Leaf lamina 10-40 cm long, 8-13(-15) cm wide, length:width ratio 1.8-3, narrowly oblong to oblong or narrowly obovate to obovate, base rounded to obtuse, apex acuminate, acumen 3-9 mm long, papery when young becoming coriaceous, glabrous; midrib glabrous on both sides; secondary veins (9-)11-16(-17) pairs, uniformally curving upwards, glabrous. Flowers single, leaf-opposed or sometimes extra-axillary, pendulous. Flowering pedicels 30-55 mm long, ca. 1 mm in diameter, glabrous, light green. Upper bract positioned centrally or sub-apical on the pedicel, 6-10 mm long, 7-11 mm wide, length:width ratio 0.6-1, depressed ovate to very broadly ovate, cup-shaped, base decurrent, apex shortly acuminate, upper and lower surface glabrous, margins straight, glabrous or sparsely to densely covered with erect hairs. Sepals reflexed upwards at anthesis, falling in fruit, 7-11 mm long, 5-10 mm wide, length:width ratio 1-1.8, very broadly ovate to ovate, base truncate, apex rounded to obtuse, glabrous, green, margins undulate, glabrous or sparsely to densely covered with short erect hairs. Inner and outer petals fused, flexed down along the pedicel for 5-7 mm before recurving upwards. Outer petals (25-)30-45 mm long, 15-30 mm wide, length:width ratio 1.5-2, oblong to ovate, base truncate, apex acute, glabrous on both surfaces, white-cream towards base, specked and streaked yellow purple, straight spreading horizontally, margins strongly undulate, glabrous to sparsely covered with short erect hairs. Inner petals (17-)20-27 mm long, (13-)15-20 mm wide, length:width ratio 1-1.6, clawed, rhomboid, base and apex acute, inside sparsely covered with erect 2-2.5 mm long hairs, glabrous on the outside, yellow with brown-purple spots, connivent along the margins over receptacle, margins straight, densely covered with short curly hairs; claw 2-5 mm long, claw:inner petal ratio 0.1-0.3, glabrous, yellow. Receptacle 4-6 mm in diameter, strongly convex. Stamens in 12-14 rows, ca. 1 mm long, densely covered with short erect hairs; connective shield 0.2 mm long, glabrous, those of innermost whorl not elongated over ovary wall. Ovary ca. 4 mm long, ca. 2 mm wide stigma 1.5-2 mm in diameter, sparsely covered with short erect hairs. Fruiting pedicels 4-5 cm long, 8-10 mm in diameter, woody, glabrous. Fruits 6-12 cm long, 4-6 cm in diameter, length:width ratio 1.3-1.8, ovoid, apex rounded, farinose, smooth, glabrous, pale brown; pericarp 4-5 mm thick. Seeds 9-20 mm long, 6-11 mm wide, transversely ellipsoid, packed in white pulp; testa smooth, light brown; raphe not thickened, dark brown; hilum 2-3 mm long, 1.5-2 mm wide, elliptical.
Monodora undulata closely ressembles M. myristica both having the uniquely strongly convex receptacles, large leaves, and completely connivent inner petals. They also exhibit the same pollen tectum surface, smooth with small perforations (Couvreur et al., 2008). However, M. undulata is distinguished from M. myristica by its smaller flowers with shorter flowering and fruiting pedicels, the cup-shaped non-undulate upper bract and the ovoid farinose fruit.
The seeds are used as flavoring for sauce, to treat coughs and eaten in a mixture with Scilla oubanghiensis Hua as an aphrodisiac (Neuwinger 2000). A decoction of the roots is taken internally to relieve urethral strictures (Neuwinger 2000). The seed are used as a condiment (Burkill 1985), or are mixed with Xylopia aethiopica for medical use (no prupose indicated, Burkill 1985).
Sierra Leone to Equatorial Guinea and the São Tomé and Principe islands; in lowland primary and secondary rain forests, along rivers and in swamps, at 0-700 m altitude.