Stenogyne angustifolia is a decumbent or scandent vine. The stems are weakly 4-angled and glabrous, except for occasional pubescence at the nodes. The leaves are simple and opposite, with narrowly ovate blades, elliptic, lanceolate, or oblanceolate. They measure 2.6–5.3 cm long and 0.6–1.5 cm wide. The apex is acute or rarely obtuse, and the base is also acute. The surfaces of the leaves are glabrous, and the blades are membranous. The margins are serrulate. The petioles are 4–16 mm long and glabrous. Stipules are absent. The flowers occur in pairs per verticillaster, either axillary or on axillary shoots, with pedicels that are 2–8 mm long and puberulent. The calyx is bilabiate and narrowly campanulate, 8–18 mm long, enlarging in fruit, glabrous, with acute teeth 5–9 mm long and 1.5–3 mm wide at the base. The calyx usually persists but may sometimes be only ventrally persistent. The corolla is bilabiate; its color can range from yellow to dull brownish pink, magenta, or red. The corolla is moderately pubescent externally and glabrous internally. The tube is narrowly funnelform, 1.1–1.9 cm long, with an upper lip that is 5–10 mm long, either entire or 2-lobed. The lower lip is about 2 mm long, 3-lobed, with flat or revolute lobes. The corolla is sparsely to densely pubescent externally with simple or multicellular hairs and is occasionally glandular pubescent inside. Stamens are 4 in number, with both pairs being of similar length or the upper pair slightly longer. The stamens are included within the corolla or exserted beyond the upper lip. The ovary is superior, and the style is exserted, diverging after anther dehiscence and shortly 2-lobed. The seeds are oily and have scanty or no endosperm. It is found in dry subalpine shrubland between 1,550–2,150 meters.