Wikstroemia oahuensis var. palustris is a densely foliaceous shrub or dwarf tree that typically reaches up to 1 meter in height. The main stem may be short, while branches range from slender to robust and are more or less erect. Branches are glabrous or have scattered hairs and usually become glabrate with age; some may remain pubescent. The bark may exhibit whitish lenticels, particularly near prominent leaf scars. The leaves are simple and opposite. Leaf blades vary in shape from narrowly to broadly elliptic, ovate–elliptic, or rarely slightly obovate, measuring (1–)2.5–8(–20) cm long and (0.5–)1.5–3(–6.5) cm wide. The apex is typically acute or rounded but may also be acuminate or slightly apiculate. The base is acute or rounded, rarely subcordate. Leaf surfaces are glabrous or pilose, especially along the midrib on the lower surface, and can be hirsute. The upper surface ranges from pale to dark green, occasionally tinged with lilac-crimson or glaucous; the lower surface is often brighter and sometimes slightly translucent. Blades are thin to firm chartaceous or coriaceous with entire margins and pinnate venation. Petioles are (2–)4–9(–13) mm long, thin or stout, and either glabrous or pilose. Stipules are absent. The flowers are borne on peduncles 2–15(–25) mm long, which may be glabrous or pilose and are sometimes recurved. The inflorescence rachis is subglobose, conical, or filiform, rarely forked, and varies from 0.4–5 mm in length (up to 12 mm when pendulous), glabrous or puberulent. Pedicels measure 0.5–7 mm and can also be glabrous or sparsely hairy. Flowers are green to yellow and can be bisexual or unisexual, sometimes appearing perfect, with the entire structure glabrous or hirsute. The calyx tube of staminate and perfect flowers is (4–)5–9(–13) mm long, with outer lobes 1.3–6 mm by 1–4 mm and inner lobes 1.2–5 mm by 1–3.6 mm. For pistillate flowers, the calyx tube is 3–10 mm long, outer lobes 1–9 mm by 1–3.8 mm, and inner lobes 1–5 mm by 1–3.8 mm. Petals are absent. There are 8 stamens arranged in two whorls, with the lower whorl included and the upper sometimes shortly exserted. The ovary is superior, 1-celled, with a single pendulous ovule. The fruits are ellipsoid, measuring 6–18 mm in length and 4–10 mm in diameter, and turn orange to red upon maturity. Seeds lack endosperm. It is found in mesic to wet forests, diverse mesic forests, bogs, ridges, and rocky ledges between (5–)100-1,400 meters.