Cyrtandra sandwicensis is a shrub that typically grows to a height of 0.5–2.5 meters. The stems are usually many-branched, rounded, or angular, covered in pubescent multicellular hairs, or are sometimes smooth (glabrate). The leaves are simple and opposite, found on the stem’s upper 3–8 nodes. The leaves within a pair are often unequal and asymmetrical, ranging in shape from broadly elliptic to elliptic or occasionally ovate, with sizes from 6.5–20 (–25) cm in length and 3.2–8(–10) cm in width. The leaf apex is acuminate, and the base is asymmetrical, tapering to an attenuate or cuneate shape. The upper surfaces of the leaves are moderately to sparsely covered with appressed pilose hairs. In contrast, the lower surfaces are dense to occasionally moderately covered with velvety short pilose hairs that are whitish. The leaves are chartaceous and have serrate to serrulate margins. Petioles range from (1.2–)2.5–9(–12.5) cm long and may sometimes clasp the stem or appear perfoliate. Stipules are absent. The flowers are typically solitary (1–3) and arise in the leaf axils. The entire flower structure is densely pilose, with peduncles (0–)5–15 mm long and pedicels 7–15 mm long, extending to 20–26 mm in fruit. The bracts are linear-lanceolate, distinct, or occasionally fused, measuring 2–7 mm long. The flowers are bisexual (perfect) and usually exhibit a bilabiate corolla that is white. The calyx is actinomorphic (radially symmetric) or nearly so, green when fresh and 7–12 mm long, splitting approximately halfway to two-thirds its length. The corolla tube is cylindrical initially and becomes narrowly ellipsoid, flaring slightly at the mouth, measuring 8–14 mm long and about 3–7 mm in diameter. It is densely covered in white pilose hairs. The corolla’s upper lip has two lobes, and the lower lip has three, with the upper lobes reniform and the lower lobes reniform-orbicular. There are five stamens, with the two upper ones being fertile and the others staminodial. The fertile anthers are coherent and positioned in the throat of the corolla tube, opening via longitudinal slits or occasionally through apical pores. The ovary is superior, oblong-ovoid, and consists of two carpels that form one chamber due to the deeply intruding placentas. The style is approximately 3 mm long, villous, and less hairy with age, and the stigma is capitated with two elliptic lobes. The fruit is a white, fleshy, or firm berry, ovoid-ellipsoid in shape, measuring 0.8–1.5 cm long and puberulent. It is often tipped by the persistent stylar beak. The seeds are numerous, ellipsoid, and minute, measuring 0.4–0.6 mm long and with a reticulate surface. It is found on moist slopes and shaded gulch bottoms within disturbed mesic valleys, often coexisting with Psidium and Aleurites between 360–520 meters.