Melicope lydgatei is a small shrub with new hirsute growth, eventually becoming glabrate. The leaves are simple, arranged oppositely or in whorls of three per node. The leaf blades range from oblanceolate to obovate or oblong, sometimes oblong-ovate, measuring 4–13 cm in length and 1.5–6.5 cm in width. The apex of the leaves varies from acute to narrowly obtuse, with some leaves featuring a rounded apex. The base is weakly cordate. The leaf surfaces are glossy and glabrous, with the blades being firm–chartaceous. The margins are entire, and the primary lateral veins, numbering between 10–15 pairs, are connected by an arched vein located 1–6 mm from the margin. The venation is pinnate, with lateral veins connected by an arched submarginal vein and forming a reticulate pattern of higher-order venation. The petioles are 0–10 mm long or up to 20 mm long when leaves are ternate. Stipules are absent. The flowers appear 1–3 in slender, glabrous, axillary cymes. The peduncles are 8–13 mm long, and the pedicels range from 8–35 mm long, with bracteoles up to 1 mm long. The flowers can be bisexual (perfect) or functionally unisexual, indicating that the plants may be monoecious. The calyx consists of 4 sepals; sepals of pistillate flowers are ovate–deltate, measure 2–3 mm in length, and are glabrous and imbricate. The corolla has four valvate petals: greenish-white, deltate, and 4–7 mm long. There are eight stamens in two whorls, distinct but reduced in functionally pistillate flowers. The ovary is superior, glabrous, 4-celled, and 4-lobed with connate carpels, slightly distinct at the apex to almost entirely distinct; each cell contains two hemitropous ovules, with one ascending. The style is slender, about 5 mm long, ending in 4 short stigmatic branches. The fruits are capsules measuring 14–22 mm wide; carpels are connate for ¼–⅓ of their length and are 7–11 mm long; both exocarp and endocarp are glabrous. The carpels dehisce along the upper suture. Seeds are 1–2 per carpel, about 5 mm long, glossy black when ripe, crustaceous, ovoid, sometimes angled from compression, with an embryo straight in fleshy endosperm. The radicle is short; cotyledons are compressed and ovate, and the putamen is brown and warty. It is found in mesic forest habitats between 410–550 meters.