Psychotria grandiflora is a small tree or shrub that can reach up to 5 meters in height. The leaves are simple and opposite, with obovate or occasionally elliptic blades, measuring 4–14.1 cm long and 1.6–6.3 cm wide. The leaf apex is obtuse to rounded, and the base ranges from acute to obtuse. The lower surfaces of the leaves are glabrous to sparsely pubescent, especially along the midrib, and are usually tinged red. The leaves are coriaceous, with small or absent domatia and revolute margins. There are 6–12 pairs of lateral veins, and the tertiary veins are conspicuous on the lower surface. Petioles measure 0.1–2 cm long, and the stipules are ovate–deltate to obovate, 5–8 mm long, with an obtuse or rounded apex and a thick band of brown hairs in the axil. The stipules are caducous. The flowers are arranged in inflorescences with a central axis and usually verticillate branching. Each branch is subtended by a bract that completely encircles the nodes. A 3-flowered cymule usually terminates the branches of the lower node, while those of the upper node, when present, often have only one flower. Peduncles are (0.5–)5–9.5 cm long and usually pubescent, with pedicels measuring 0.1–0.6 cm long. The bracts are usually found on secondary inflorescence branches, are ovate, less than 1 mm long, and brown villous within. The flowers are insect-pollinated, functionally unisexual, 5-merous, and often heterostylous. The calyx is 1–2 mm long, slightly dilated toward the apex, and truncate. The corolla is white, with a tube measuring 10–22 mm long, dilated somewhat toward the apex, with a glabrous throat, and ovate–deltate lobes 4–6 mm long that are reflexed. A nectary disk is present at the apex of the ovary. The stamens are as many and alternate with the corolla lobes and are exserted at anthesis. The filaments are usually inserted on the corolla tube or throat, measuring 3–4.5 mm long. The anthers are exserted at anthesis in functionally staminate flowers, attached ¼–⅓ from the base, 3.5–4.5 mm long, dithecal, and open by longitudinal slits. The ovary is inferior, occasionally partly so, or rarely superior, 3–4 mm long at anthesis, 2-celled, with basal placentation. Ovules are 1 per cell, erect, and anatropous. The style is as many as the carpels, 20–28 mm long, terminal, and slender. The stigmas are 2, small, lobed or capitate, divergent in pistillate flowers, appressed in functionally staminate flowers, pubescent, and dry or occasionally wet. The fruit is drupaceous, orange, usually pyriform, and 10–15 mm long at maturity. It is capped by the persistent calyx tube, which is 1–2 mm long. The fruit contains 1-2(-4) pyrenes that are triangular in cross-section and usually lack invagination of the seed coat on the ventral surface. The endocarp is usually thick and hard. There is one seed per pyrene, conforming to the form of the pyrene. The seed coat is thin and usually without invagination on the ventral surface. The endosperm is carnose, and the embryo is small with flat, thin cotyledons. The seeds have well-developed oily endosperm, or the endosperm is occasionally scanty or absent. It occurs in mesic to sometimes wet forests between 1,040–1,230 meters.