Cyrtandra polyantha is a shrub growing 1–3 meters tall. The stems are unbranched to few-branched, rounded to angular, and pubescent with multicellular hairs or glabrate. The leaves are simple, opposite, and borne on the upper 5–10 nodes. The leaves of a pair are unequal, symmetrical, and elliptic, measuring 5–16 cm long and 1.8–5.2 cm wide. The leaf apex is acute, and the base is cuneate to attenuate. The upper surfaces of the leaves are glabrous to sparsely bullate hirsute, while the lower surfaces are moderately to densely pale brownish puberulent. The blades are coriaceous, and the upper surfaces are conspicuously rugose. The margins are serrulate and often revolute, with principal veins strongly impressed on the upper surface. The petioles are 1–5 cm long, with the base sometimes clasping the stem or perfoliate. Stipules are absent. The flowers are 7–12 in subumbelliform, branched cymes arising in the leaf axils, sparsely puberulent, becoming glabrate. The peduncles are 12–18 mm long, and the pedicels are slender, 3–19 mm long. The bracts are lanceolate, distinct, or occasionally connate, 3–10 mm long. The flowers are bisexual (perfect). The calyx is 2–5(6)-lobed, nearly actinomorphic (radially symmetric), greenish-white when fresh, 4–6 mm long, cleft 1/2–2/3 its length. The lobes are narrowly deltate, sparsely puberulent, glabrous within, and deciduous or persistent in fruit. The corolla is usually bilabiate and white, with a cylindrical tube that is straight or curved, 11–13 mm long, enlarging to 6–8 mm in diameter medially, and densely appressed short-villous. The upper lip is 2-lobed, and the lower lip is 3-lobed, with the lobes imbricate in bud. The upper lobes are broadly rhombic, 3–4 mm long, and 4–5 mm wide, while the lower lobes are broadly rhombic-ovate, 4–5 mm long, and 5–7 mm wide. Five stamens are inserted about halfway up the corolla tube, with the two upper stamens being fertile and the others staminodial, often with abortive anthers. The fertile anthers are coherent, positioned in the throat of the corolla tube, dithecal, and open by longitudinal slits or occasionally by apical pores. The ovary is superior, oblong-ovoid, 2-carpellate, and 1-celled, with parietal placentation. The placentas are 2, somewhat intruded, and rarely joined in the center, dividing the ovary into two cells. The ovules are numerous, anatropous, and glabrous, with a rounded apex or a stylar beak. The style is 1–2 mm long, glabrous to sparsely puberulent, and the stigma is capitate, 2-lobed, with lobes usually elliptic. The fruit is a fleshy or firm berry, white, ovoid, 1.5–1.7 cm long, glabrous, and often tipped by the persistent stylar beak. The seeds are numerous, ellipsoid, and minute, measuring approximately 0.45 mm long, with a reticulate surface. It is found in disturbed mesic valleys at elevations between 490-610 meters.