Smilax melastomifolia is a liana characterized by its tuberous rhizomes. The stems are finely grooved and range from smooth to densely prickly with short-conical prickles. The leaves are simple and alternate. Leaf blades vary in shape, typically ranging from cordate to broadly ovate, occasionally suborbicular, or oblong-ovate to lanceolate, measuring (5–)7–18 cm in length and (3.3–)4–18.4 cm in width. The apex is usually abruptly acuminate to cuspidate, with bases ranging from cordate to occasionally subcordate. Leaf surfaces are glossy and glabrous, with a coriaceous texture. Margins are entire, with 5–17 principal veins that are sometimes prickly on the lower surface. Venation is conspicuously reticulate on the lower surface. Petioles are twisted and strongly curved, 1.1–3 cm long, with a pair of tendrils arising about three-quarters from the base; the petiole is slightly winged below the tendrils. Stipules are absent, but tendrils are often interpreted as stipular structures. The flowers appear in umbels of about 10–20 per umbel, axillary to the upper leaves. Peduncles are compressed, 14–30 mm long, with an ovate bract 4–8 mm long at the base. Pedicels are 6–15 mm long, each bearing an ovate bracteole about 2 mm long at the base. The flowers are unisexual with a perianth composed of 6 tepals in two series, pale green to greenish white, oblong-elliptic to oblong-oblanceolate, 8–12 mm long. Staminate flowers feature spreading tepals and (6–)12–18(–20) slightly exceeding tepals’ stamens, with linear anthers that become curved or twisted. Pistillate flowers have revolute tepals and staminodes. The ovary is superior and 3-angled, with (1)2 pendulous ovules per cell. The fruit is a globose berry, approximately 6–7 mm in diameter. It is found in mesic to wet forests and on the margins of bogs between 180-2,080 meters.