Pipturus kauaiensis is a shrub growing 1.5–3 meters tall with slender branches covered in brown bark. These branches are initially puberulent with fine, appressed white hairs, becoming glabrate with age. The stems contain watery sap. The leaves are simple and alternate, with blades that are ovate to broadly lanceolate and deeply 2-lobed, measuring 6–18.5 cm long and 2–6.5 cm wide. The apex is long-acuminate and usually slightly oblique, while the base is rounded to cuneate. The surfaces are finely strigillose with white hairs, becoming glabrate as they age. The veins are moderately strigillose, and the areoles are densely covered in white woolly pubescence, completely obscuring the surface. The upper surfaces are dark green and nearly smooth, with small and inconspicuous cystoliths. In contrast, the lower surfaces are pure white and usually appear glaucous, contrasting sharply with the white areoles. The petioles are strigillose and white strigillose toward the base of the lobe, measuring (1–)1.5–4.5(–6.5) cm long. The stipules are chartaceous, about 6.5 mm long and 5.5 mm wide. The leaves’ margins are regularly coarsely serrated, and the veins are slightly raised. The flowers are clustered in groups of about 3–4 mm in diameter, usually dimorphic, with larger pistillate clusters. The plant is gynodioecious, with puberulent and unisexual flowers. The calyx of staminate flowers is 2–2.4 mm long, while the pistillate calyx is about 1 mm long, enlarging to 1.4–1.5 mm long in fruit and hirsute. There are no petals. In staminate flowers, the filaments are incurved in the bud and elastically reflexed when pollen is shed. The anthers are dithecal and open by longitudinal slits. The pistillate flower has a superior ovary, which is pseudomonomerous (one fertile carpel and more or less prominent traces of sterile carpel(s)) and 1-celled, with a single basal ovule and one style. In staminate flowers, the ovary is vestigial and sterile. The fruit is a pale brown or gray ovoid achene, measuring 0.9–1 mm long and constricted below. There is one seed per achene. It occurs in mesic valleys and diverse mesic forests between 60 – 1,280 meters.