Charpentiera ovata var. niuensis is a slender or shrubby tree that can reach heights of 4.5 to 6 meters, characterized by new pale brown growth and tomentose. The stems are slender, measuring 0.5 to 5 mm in diameter near the apex, with internodes ranging from 1.6 to 14 mm in length. The leaves of this variety are simple and alternate, with blades that are nearly elliptic or suborbicular, measuring 5 to 18 cm in length and 3 to 13 cm in width. The apex of the leaves ranges from acute to obtuse, occasionally acuminate, while the base is usually acute. The leaf surfaces can be glabrous or pubescent, and the blades are somewhat coriaceous. The margins are entire and typically lack developed marginal ribs. There are 10 to 20 pairs of lateral veins, and the petioles are 1 to 7 cm long. Stipules are absent. The flowers are arranged in single axillary panicles, which can be 1 to 2 branched, either reddish brown pubescent or glabrous. The panicles are 12 to 40 cm long, simple or compound, with 5 to 15 primary branches. A bract subtends each branch. The plant is gynodioecious (having some individuals bearing female flowers only and others bearing hermaphrodite flowers only), with populations consisting of both bisexual (perfect)–flowered plants and female plants. There are several to numerous flowers per branch, with internodes between individual flowers measuring 1 to 5 mm long. The calyx comprises five distinct, imbricate, subequal sepals that are 1.5 to 2.25 mm long and discernibly 3 to 7-veined. The corolla (petals) is absent. There are five stamens and staminodes, with filaments forming a short, membranous tube, and the anthers are exserted at anthesis. The ovary is superior, globose or urceolate, 1.5 to 2 mm long, with an absent or concise style and two straight or recurved stigmas nearly as long as the ovary, with glands on the inner surface. The fruit is an indehiscent utricle, and the seeds are black, shiny, lenticular, and approximately 1.5 mm long at maturity. It is found in wet and mesic forests at elevations ranging from 180-1,160 meters.