Cyrtandra sessilis is a shrub reaching heights of 0.5–1 m. Its stems are branched, rounded, or angular, and can be pubescent with multicellular hairs or glabrate. The leaves are arranged in three whorls per node and found on the stem’s upper 3–9 nodes. Each leaf is symmetrical and oblanceolate, measuring 8–20 cm long and 2–6.4 cm wide. The leaves’ apex is acuminate, while the base is oblong and often auriculate. The upper surfaces of the leaves are sparsely appressed pilose along the midrib when young but are otherwise glabrous. The lower surfaces are sparsely appressed pilose along the veins. The leaves are thick and chartaceous, with subentire or occasionally serrulate to crenate margins on the upper half. The leaves are sessile, with some bases clasping the stem or being perfoliate. There are no stipules present. The flowers occur in cymes of 3–8, arising from the leaf axils. These cymes are appressed to spreading brown pilose throughout, with peduncles measuring 1–7 mm long and pedicels 3–10 mm long. The bracts are narrowly lanceolate to linear, distinct, or occasionally connate, measuring 4–9 mm long. The flowers are bisexual (perfect) and feature a calyx that is 2–5(6)-lobed, zygomorphic (bilaterally symmetric), broadly fusiform in the bud, and tipped by a 2–3 mm long beak. When open, the calyx is pale green and chartaceous, measuring 14–27 mm long, with the tube ranging from 13–18 mm. The calyx is glabrous except for sparse pilosity toward its base, with the upper three lobes measuring 9–11 mm long and the lower two lobes around 7–9 mm long. The corolla is usually bilabiate and white, with a narrow funnelform tube that is curved near the middle and measures 15–24 mm long and 5–7 mm in diameter. It is glabrous, with a two-lobed upper lip and a three-lobed lower lip; the lobes imbricate in bud. Five stamens are inserted about halfway up the corolla tube, with the two upper stamens fertile and the others staminodial. The fertile anthers are coherent and positioned in the throat of the corolla tube, dithecal, opening by longitudinal slits or occasionally by apical pores. The ovary is superior, oblong–ovoid, 2-carpellate, 1-celled, with parietal placentation; it is glabrous with a rounded apex or stylar beak, and the style measures approximately 6–7 mm long. The fruit is a white, fleshy, or firm berry, ellipsoid in shape, approximately 1.4–1.6 cm long, and often tipped by the persistent stylar beak. The seeds are numerous, ellipsoid, minute, measuring 0.3–0.4 mm long, with a reticulate surface. It is found in wet gulch bottoms and on slopes in mesic valleys and wet forests between 480-610 meters.