Strongylodon ruber is a glabrous liana with herbaceous branches. The leaves are compound (pinnately trifoliate) and alternate, tardily deciduous. The leaflets are broadly ovate to broadly rhombic–ovate or ovate, with the lateral ones usually asymmetrical, measuring 6.5–12.5 cm long and 3.8–10.5 cm wide. The leaflets have a short-caudate or long-caudate apex and are glabrous with membranous surfaces that become chartaceous when dry. The leaflets’ margins are entire and tripliveined, with several additional pairs of lateral veins and reticulate tertiary venation. The petioles are 6–10 cm long. Stipules are present, ovate or deltate, 2–5 mm long, persistent, and conspicuous. Leaflet stipels are linear, 2–6 mm long. The flowers are usually 2–3 per cluster in pendulous axillary pseudoracemes 25–45 cm long. They are papilionaceous and elongated, suited for bird or bat pollination. The bracts are small, with orbicular or ovate bracteoles that are small and caducous. The pedicels are 15–45 mm long. The calyx is 5-lobed and campanulate, 6–9 mm long, with the upper two lobes connate into an emarginate lip, and the other lobes are 1.5–2.2 mm long with overlapping margins at the base. The corolla is bright scarlet, with the standard being ovate-oblong with two appendages above the claw, becoming reflexed, 33–37 mm long. The wings are 15–20 mm long, much shorter than the standard, and adhere to the keel. The keel petals are 30–36 mm long. There are ten stamens; the upper stamen is distinct, and the other nine are connate into a tube. The ovary is superior and stipitate with usually two ovules. The style is filiform and glabrous, apically, with a slight, terminal stigma. The fruit consists of stipitate pods, obliquely ovoid or ellipsoid to oblong–ellipsoid, often sigmoid, measuring 3–12 cm long and 4.5–6 cm wide. The pods are indehiscent with strongly veined valves. The seeds are 1–2 per pod, black, subglobose, and compressed, 2.3–3.3 cm in diameter, with the hilum being ⅓–½ the circumference of the seed. It climbs and hangs from trees in mesic to wet forests between 180-825 meters.