Phyllostegia glabra var. glabra is an erect to decumbent perennial herb with stems ranging from 1-5 m in length, which are glabrous. The leaves are simple, opposite, and vary in shape from ovate to oblong-lanceolate, measuring 8–24 cm in length and 2.5–10.5 cm in width, with a long-acuminate apex and a broadly cuneate to rarely subcordate base. The leaf surfaces are glabrous, often red-tinged or with red veins, glossy on the upper side, pale and membranous on the lower side, and the margins are serrated. It features flowers 6–10 per verticillaster, forming unbranched, bracteate, racemose inflorescences 15–45 cm long. These inflorescences develop terminally on branches, with pedicels slender and 5–15 mm long. The calyx is obconical, 4–11 mm long, glabrous, and usually has five narrowly deltate teeth. The corolla is bilabiate, white, sometimes tinged with reddish-purple, with a size-variable tube and slightly folded lobes to form a groove. It has four stamens with a somewhat longer upper pair in the corolla tube. The ovary is superior, with basal-axile placentation and a single ovule per ovary lobe. The style is included, shortly 2-lobed, with one lobe often rudimentary. The fruit is drupaceous, 4–5 mm long, dark green to black nutlets with a fleshy exocarp and slightly winged margins. The seeds are small and lack an endosperm or are scanty and oily. It grows in mesic to wet forests between 275-1,190 meters.