Kadua elatior is a lax, branched subshrub, often forming clumps or mats. The stems are ascending to weakly erect, nearly terete (cylindrical) to quadrangular, more or less slightly striate, and usually 10–20 centimeters long. The leaves are simple, opposite, and range from linear–elliptic to linear–lanceolate, though they can also be very narrowly elliptic or very narrowly lanceolate, usually falcate. They measure 4–18 cm long and 0.6–1.5 cm wide. The apex is long–attenuate, and the base is also long-attenuate. The surfaces are glabrous, thin, and chartaceous. The margins are entire, flat to slightly revolute. Lateral veins appear in one to a few pairs, subparallel to the midrib, while higher-order venation is obscure. The petioles are 0–0.6 cm long and connate at the base into a 4–6 mm long sheath. Stipules are linear with a broadly deltate base, measuring 5–7 mm long, adnate to the petiole sheath, with the linear apical part 3.4–5 mm long. The flowers are arranged in compound, terminal, monochasial cymes, and are glabrous throughout. Pedicels measure 4–15 mm long, and the bracts subtending the inflorescence are linear–lanceolate, about 2–4.5 cm long. The hypanthium is turbinate, about 0.5–1.6 mm long. The flowers are insect-pollinated and, bisexual (perfect) and pistillate. The calyx is 4- to 5-lobed, with linear lobes–deltate or rarely narrowly deltate, 2.5–7 mm long and 1–1.5 mm wide, enlarging to 4–16 mm long in fruit. The corolla is white to green or sometimes purplish, fleshy, and salverform, with the tube enlarging somewhat at the throat, measuring 8–17 mm long. The limb is not strongly quadrangular in bud, but the apex is depressed, and the lobes are 3–4 mm long at anthesis, strongly inflexed in bud. A nectary disc is present. The stamens are as many and alternate with the corolla lobes, inserted 1–3 mm below the corolla lobe sinuses. The anthers are sessile or on short filaments, dithecal, and open by longitudinal slits. The ovary is inferior or partly so, with 2(-4) locules. The ovules are few to numerous on fleshy placentas near the middle of the septum. The style is as many as the carpels, cylindrical to filiform, terminal, long-villous in the lower two-thirds, with the apex 2-lobed. The stigma is bilobed or subcapitate, either included or exserted. The fruit consists of turbinate capsules measuring 3–6 mm long and 4–5 mm in diameter, dehiscing loculicidally across the disk. The pyrenes tardily dehisce across the disk and slightly further septicidally. The endocarp is thinly sclerified, and the disk is slightly raised. The seeds are dark brown, cuneiform, irregularly angled, with well-developed oily endosperm, though the endosperm is occasionally scanty or absent. It occurs in wet sites, usually on cliff faces, streambeds, waterfalls, and sometimes in running water between 120-1,100 meters.