Cyrtandra waianaeensis is a shrub that grows to a height of 1–7 meters. The stems are branched, rounded to angular, and pubescent with multicellular hairs or glabrate. The leaves are simple and opposite, usually borne on the upper 3–5 nodes. The leaves of a pair are somewhat unequal to subequal, asymmetrical to symmetrical, very broadly elliptic to suborbicular, or occasionally very broadly ovate, measuring 9–27 cm long and 3–9.5 cm wide. The leaf apex is acuminate, occasionally obtuse or rounded, and the base is truncate to broadly cuneate. The upper surfaces are sparse to moderately hirtellous, while the lower surfaces are moderately velvety pilose, with villous veins and yellowish-brown hairs. The leaf blades are chartaceous, with denticulate margins to subentire or sometimes serrate. The petioles are 3–10 cm long, with the base sometimes clasping the stem or perfoliate. Stipules are absent. The flowers are arranged in (2)3–5 open umbelliform cymes arising in the leaf axils, densely villous throughout. The peduncles are 10–50(–70) mm long, and the pedicels are 10–30 mm long, elongating to 30–50 mm long in fruit. The bracts are large, whitish-green, foliaceous, asymmetrical, narrowly ovate, distinct or occasionally connate, and measure 9–100 mm long. The flowers are bisexual (perfect). The calyx is 2–5(6)-lobed, nearly actinomorphic (radially symmetric), whitish-green, broadly saucer-shaped, often reflexed in fruit, 8–19 mm long, cleft about half to two-thirds its length, with deltate to ovate lobes that are densely villous and have acuminate to caudate apices. The corolla is white bilabiate with a cylindrical tube that flares slightly at the mouth, is 14–16 mm long, and is about 5–7 mm in diameter medially. It is densely villous, with lobes that are erect to slightly spreading. The upper lip is 2-lobed, and the lower lip is 3-lobed, with lobes imbricate in bud. The upper lobes are broadly rhomboid, 2–3 mm long and 3.5–5 mm wide, while the lower lobes are broadly ovate, 3–5 mm long and 3.5–5.5 mm wide. There are five stamens inserted about halfway up the corolla tube. The two upper stamens are fertile, while the others are staminodial, 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, 1-celled, with parietal placentation. The placentas are 2, intruded, and rarely joined in the center, dividing the ovary into two cells. The ovules are numerous, anatropous, and moderately villous, with a rounded apex or a stylar beak. The style is about 3–4 mm long and densely villous, with a capitate, 2-lobed stigma, the lobes usually elliptic. The fruit is a fleshy or firm berry, white, ovoid, 1.5–2 cm long, densely villous, often tipped by the persistent stylar beak. The seeds are numerous, 0.5–0.6 mm long, ellipsoid, with a reticulate surface. It is found in moist, shaded gulch bottoms in disturbed mesic valleys, diverse mesic forests, and wet forests between 460 – 1,100 meters.