Kadua fluviatilis, a member of the Rubiaceae (coffee) family, is a scandent (climbing) shrub, foetid (bad smelling) when bruised; with cylindrical, but slightly flattened, stems, 0.3 to 2.5 m (1 to 8 ft) long, glabrous (hairless), and with short lateral branches. Leaves are widely spaced, papery, elliptic-oblanceolate to elliptic-lanceolate (narrowly oval to lance-shaped), 8 to 17 cm (3.2 to 6.8 in) long, and 3 to 5 cm (1.2 to 2 in) wide. Flowers are perfect and pistillate (hermaphrodite and female), borne in reduced axillary, cymose inflorescences. Calyx lobes are deltate to narrowly ovate (triangular to egg-shaped), 12 to 18 mm (0.5 to 0.7 in) long, 3 to 6 mm (0.1 to 0.2 in) wide, with several small sac-like glands between corolla lobe sinuses. The corolla is white, fleshy and waxy, with a tube 22 to 30 mm (0.9 to 1.2 in) long. Capsules are woody, strongly quadrangular or winged, 8 to 13 mm (0.3 to 0.5 in) long, and 9 to 13 mm (0.4 to 0.5 in) in diameter. Seeds are translucent reddish brown, wedge-shaped, and minutely reticulate (net-veined).