Kadua parvula is a small, erect to, sprawling, glabrous, many-branched shrub. The stems are 4-angled or 4-costate, measuring 1–3(–4) decimeters long. The leaves are simple and opposite, usually closely spaced and overlapping, and do not become reduced above. The blades are lanceolate to ovate-cordate, 1–4 cm long, and 0.7–2.3 cm wide, with glabrous, coriaceous surfaces. The margins are entire and slightly revolute, with lateral veins strongly ascending. The petioles are 0–0.2 cm long. The stipules are deltate, strongly carinate, 2–3 mm long, with a mucronate apex. The flowers are in narrow corymbose inflorescences, sometimes appearing as one larger inflorescence due to several contiguous branches with 2–8 mm long pedicels. The inflorescences are subtended by a pair of cordate bracts 0.6–1.5 cm long. The hypanthium is turbinate to cup-shaped, 1–1.5 mm long. Flowers are bisexual (perfect) or pistillate, with a calyx that is 4-5-lobed, lobes weakly foliaceous, bluntly ovate, 1–4 mm long, and 1–2 mm wide, often variable in size on a single plant, enlarging to 4.5–5.5 mm long in fruit. The corolla is 4-5-lobed, white, tinged purplish pink toward the tips, fleshy, and salverform-funnelform, with a tube 8–11 mm long and a limb not quadrangular in bud but with a depressed apex, the lobes are 5–6 mm long and inflexed. A nectary disc is present. Stamens are as many as and alternate with the corolla lobes, sessile, attached slightly below the corolla throat; anthers are sessile or on short filaments, dithecal, opening by longitudinal slits. The ovary is inferior or partly so, 2(-4)-locular, with few to numerous ovules on fleshy placentas near the middle of the septum. The style is as many as carpels, cylindrical to filiform, enlarged in the upper part, woolly pubescent near the middle with long and crinkly hairs, slightly 2-lobed, and terminal; the stigma is bilobed or subcapitate, included or exserted. The fruit is a subglobose capsule, ca. 3.3–4 mm long and ca. 3.5–4 mm in diameter, dehiscing loculicidally across the disk and later ca. ½ to the base, with pyrenes separating septicidally. The endocarp is moderately sclerified, and the disk is slightly raised. The seeds are dull brown, subpeltate, bluntly angled, and darkly granulate under high magnification, with well-developed oily endosperm, though occasionally, the endosperm is scanty or absent. It is found on cliff faces, rock outcrops, and ledges between 715 – 825 meters.