Wikstroemia bicornuta is a straggling shrub to small tree that can grow 1–2.5(–7) meters tall. The young branches can be hirsute or glabrous. The leaves are simple and opposite, with elliptic to broadly ovate or suborbicular blades that are (2–)3.5–8(–10) cm long and (1.5–)2.5–4.5(–6) cm wide. The leaf apex is obtuse to broadly rounded, and the base is similarly shaped, though it can occasionally be slightly acute with a tapering base. Leaf surfaces can be pubescent or have scattered hairs at least along the midrib and lateral veins, though sometimes they are glabrous. The petioles are dark green on the upper surface, lighter on the lower surfaces, and pubescent. The blades are chartaceous with entire margins and pinnate venation. Petioles are 3–12 mm long, and stipules are absent. The flowers occur on thick peduncles about 3 mm long, which are hirsute. The rachis is subsessile, 2–10 mm long, and hirsute, with 0.5–3.5 mm long pedicels. The flowers are unisexual and greenish, with pubescent or sparsely pilose surfaces. The calyx tube of staminate flowers is (5–)8–13 mm long, with outer lobes 2–4.5 mm long and 1.5–3.8 mm wide, and inner lobes 1.8–3 mm long and 1.5–3.5 mm wide. The calyx tube of pistillate flowers is (4–)6.5–9.5 mm long, with outer lobes 2–4.5 mm long and 1.7–3.2 mm wide, and inner lobes 1.2–3 mm long and 1.2–3 mm wide. The lobes are somewhat fleshy. There are no corolla (petals). There are eight stamens, with the lower whorl included and the upper whorl sometimes shortly exserted. The ovary is superior and 1-celled, with solitary and pendulous ovules. The seeds are approximately 8 mm long and 5 mm wide and lack an endosperm. It is found in wet forests between 900-1,050 meters.