Coprosma rhynchocarpa is a small, dioecious tree 3-15 m tall with many-branched, drooping stems that are densely or sparsely hirsute to occasionally glabrate. The species presents simple, opposite leaves with elliptic to elliptic–oblanceolate or obovate blades measuring 55 to 150 mm long and 21 to 50 mm wide. The leaf apex is typically acuminate, occasionally acute, and subtly mucronulate, with an attenuate to cuneate base. The leaf surfaces vary, with the upper side being glabrous or sparsely to moderately covered in coarse tan pilose along the midrib and the lower surfaces ranging from densely to sparsely covered in similar pilosity, particularly along the midrib and lateral veins, though they may also be glabrous. Margins are entire, with pinnately veined patterns, and petioles are usually pilose, extending 9–28 mm in length. The flowers appear in clusters of 3–6, exhibiting a (5)6–8-merous structure with tan pilose to glabrous peduncles measuring 2.5–16 mm long. The species is dioecious and often heterostylous, attracting insect pollinators. The calyx varies between the staminate and pistillate flowers, with the former being cup-shaped and slightly bilabiate and the latter urceolate. The corolla also differs, funnelform in staminate flowers and narrowly funnelform in pistillate flowers, with a nectary disk usually present in both. The fruit is drupaceous, juicy, and bright yellowish-orange or yellowish-red, forming an ovoid shape 7–13 mm in length, topped with a conspicuous persistent calyx. It houses 2(-4) one-seeded, planoconvex pyrenes, and seeds are endowed with a well-developed oily endosperm, though it can sometimes be scant or absent. Habitat preferences span mesic to wet forests, with occasional sightings in subalpine woodland environments between 490-2,260 meters.