Cyrtandra grandiflora is a shrub that grows to heights of 1–2 meters. The stems are few-branched, rounded to angular, and may be pubescent with multicellular hairs or nearly glabrous. The leaves are simple, opposite, and occasionally arranged in whorls of three per node, appearing on the upper 3–8 nodes. They are usually unequal at each node, symmetrical or nearly so, and range from elliptic to broadly elliptic or ovate, measuring 7–36 cm in length and 2.5–7(–12) cm in width. The leaf apex is acuminate, while the base may be cuneate, sometimes abruptly constricting to an attenuate base. The upper surfaces of the leaves are very sparsely strigose to almost smooth, and the lower surfaces range from moderately to densely puberulent along the veins, becoming less so elsewhere. The leaf texture is thin and chartaceous, with margins that are entirely to occasionally serrulate in the upper half. Veins are slightly raised on both surfaces. Petioles, measuring 1.2–7(–12) cm, may clasp the stem or be perfoliate. Stipules are absent. The flowers occur in groups of 1–5(–7) within often compound cymes that arise in the leaf axils and occasionally along the stems. These inflorescences are puberulent to pilose with dark brown hairs, featuring slender peduncles 15–90 mm long and pedicels 4–13 mm long. The green, foliaceous bracts are ovate to lanceolate, either distinct or occasionally fused and measure 16–66 mm long, typically falling off late. The flowers themselves are perfect, featuring a zygomorphic (bilaterally symmetric), fusiform calyx in bud, which becomes pale green and thin in anthesis, measuring 18–21 mm in length, eventually falling off after the flowers bloom. The corolla is usually bilabiate and white, curving near the middle, with a subcylindrical tube 20–23 mm long and about 6 mm in diameter at the middle. The corolla’s upper lip is 2-lobed, and the lower lip is 3-lobed, with the lobes imbricating in bud. Stamens number five, with the upper two being fertile and positioned halfway up the corolla tube, with dithecal anthers that open either longitudinally or occasionally by apical pores. The ovary is superior, glabrous, oblong-ovoid, and 2-carpellate, with numerous anatropous ovules. The style is about 7 mm long and glabrous, and the stigma is capitate and 2-lobed. The fruit is a white, ellipsoid berry, 2–2.5 cm long, smooth, and often tipped by the persistent stylar beak. It contains numerous tiny, 0.2–0.3 mm long ellipsoid seeds with a reticulate surface. It is found in wet gulch bottoms and lower slopes in disturbed mesic valleys and wet forests between (180–)300–540 meters.