Pipturus ruber is a shrub that grows between 1.5 and 2 meters tall. The branches have reddish-brown bark and are hispid, with hairs approximately 1 mm long, accompanied by red-tipped glands. The leaves are simple, alternate, and widely spaced, with ovate to elliptic blades measuring 7.5–18(–25) cm long and (3.5–)4.5–7 cm wide. Young growth leaves can reach up to 31 cm in length and 20 cm in width. The leaf apex is acuminate, while the base is rounded to broadly cuneate. The upper surfaces are pale green and smooth, with slightly impressed veins, flat or slightly raised intercostal areas, and sparse pubescence that becomes glabrate with age. The lower surfaces are gray to olive gray, with thinly woolly pubescent areoles and coriaceous blades. The margins are coarsely crenate, and the palmately 3-veined or 5-veined leaves transition to pinnate venation near the apex. The veins are bright red and raised, with moderate to dense hispidity, including spreading hairs and numerous red-tipped glands. The petioles are (1–)2–7.5 cm long, and the stipules are persistent, measuring 10–12 mm long and 5–6 mm wide, with hispid veins. The flowers form clusters 8–9(–12) mm in diameter, with a few staminate flowers mixed with the pistillate ones. The plants are unisexual and appear to be gynodioecious, as no purely staminate plants have been observed. The calyx of the staminate flowers is herbaceous, 4-lobed, 2–2.2 mm long, and long-hirsute. The pistillate calyx is red, measuring 1.2–1.3 mm long and enlarging to 1.8–2.2 mm in fruit, remaining densely long-hirsute. The corolla (petals) is absent. The filaments are incurved in bud and elastically reflex when pollen is shed. The anthers are dithecal and dehisce by longitudinal slits. In pistillate flowers, the ovary is superior, pseudomonomerous, and 1-celled, with a single basal ovule and one style. The ovary in staminate flowers is vestigial and sterile. The fruit consists of pale yellow or grayish-brown achenes that are conical–ovoid and 1.1–1.5 mm long, each containing a single seed. It is found in mesic valleys, diverse mesic forests, and wet forests between 200-1,370 meters.