Schiedea diffusa subsp. diffusa is a reclining or weakly climbing vine. The stems are often swollen at the nodes and can be terete (cylindrical), 4-angled, or ridged. The primary stems range from 3 to 6 meters (up to 10 meters) long and are glabrous or nearly below, with antrorsely puberulent inflorescences. The hairs are usually reddish-purple and 0.1 to 0.4 mm long. The leaves are simple and opposite, with lanceolate to ovate or oblong-elliptic blades that are 4–12 cm long and 1.5–4 cm wide. The leaf apex is acute to attenuate, and the base is often connate around the stem, with an acute to broadly obtuse base. The blades are coriaceous, green to yellowish-green, with only the midvein evident. The margins are slightly thickened with a few scattered minute excrescences, each usually bearing a retrorsely hooked hair 0.01–0.15 mm long. The midvein is slightly excentric, with a weakly looping vein near the margins. The petioles are 0.2–0.7 cm long, and stipules are absent. The flowers are arranged in inflorescences with 20–92 flowers, measuring 10–50 cm long. The internodes and pedicels are often purple or purple-tinged. The pedicels are 8–20 mm long at anthesis, elongating to 20–40 (up to 50) mm long in fruit. The flowers are bisexual (perfect), potentially outcrossing, and protandrous (male reproductive organs mature before the female). The sepals are 5–7 mm long, strongly reflexed, and convex in the proximal quarter, producing a transverse bulge. The distal part is shallowly concave to shallowly navicular, oriented at a 30° to 60° angle to the pedicel. The corolla (petals) is absent. The staminal filaments are dimorphic, with the antisepalous whorl measuring 6.4–9 mm long and the alternate whorl 5–7.5 mm long. The ovary is superior and 1-celled, with free-central ovule placentation and 3–5 styles. The fruit is a 5–7 mm long capsule and broadly ovoid. The seeds are numerous, 0.9–1.2 mm long, suborbicular, asymmetrical, and compressed, with a smooth surface with minute depressions under high magnification. The seeds are persistent on the placenta and retained in the un-dehisced capsule. The perisperm is starchy and hard, with true endosperm absent. It is scattered in wet montane forests between 915-2,050 meters.