Kadua coriacea is a small, erect shrub that sometimes appears succulent and woody only at the base. The stems are slightly woody toward the base, with a basal leafy portion that is decumbent (growing along the ground). The stems are quadrangular, up to 3 meters long, with a corky epidermis that is longitudinally grooved. The leaves are simple and opposite, clustered toward the base of the stem. The blades are broadly ovate to broadly elliptic and fleshy, measuring 5.5–15 cm long and 3.5–7.5 cm wide. In some cases, blades may be elliptic to oblong, rarely ovate or lanceolate, and 3–8 cm long by 1.5–3 cm wide. The apex is obtuse, and the base is cuneate to rounded. The upper surfaces are dark green and glossy, while the lower surfaces are somewhat glaucous, sparsely, and minutely white scabrous. The upper surfaces are usually glabrous or rarely hispidulous, while the lower surfaces may be glabrous, hirtellous, or hispidulous. The leaves are coriaceous (leathery), with entire margins. The higher-order venation is prominently reticulate on the lower surface. Petioles are 0.5–1 cm long, with a base that expands and connates into a sheath. Stipules are broad and deltate, up to 3.5 mm long, adnate to the sheath, with an acuminate apex and mucronate, with a mucro of about 1.5 mm long. The flowers are few and occur in terminal corymbose cymes. The hypanthium is turbinate, about 0.5 mm long. The flowers are insect-pollinated and bisexual (perfect). The calyx is 4- to 5-lobed, with deltate lobes that are 0.5–0.7 mm long. The corolla is fleshy and salverform, either glabrous or hirtellous, with a tube 5–10 mm long. The limb is quadrangular in bud, with a depressed apex, 4- to 5-lobed, and lobes about 3 mm long. The lobes are inflexed in the bud, each with an inward-pointing appendage about 0.5 mm long. Stamens are as numerous as the corolla lobes, alternate with them, and inserted on the corolla throat. They are slightly exserted by the spreading corolla lobes, with anthers that are sessile or on short filaments, dithecal, and open by longitudinal slits. The ovary is inferior or partly so, 2(-4)-locular, with ovules located on fleshy placentas near the middle of the septum. There are as many styles as carpels, cylindrical to filiform, and densely woolly-pilose in the lower third. The stigma is bilobed or subcapitate, included or exserted. The fruit is a lenticular capsule, approximately 2.5–3 mm long and 7–8 mm wide. It dehisces loculicidally across the disk, with pyrenes tardily separating septicidally. The mesocarp is dry, and the endocarp is weakly sclerified. The disk is slightly raised. Seeds are dark brown, compressed, irregularly angled, and contain well-developed oily endosperm, though the endosperm is occasionally scanty or absent. It is found on steep, rocky slopes in dry to mesic shrublands or forests.