Cyanea horrida is a palm-like tree species that reaches heights of 1–4 meters. The leaves are simple and alternate, with pinnately parted or divided blades, especially in juvenile plants. The blades measure 20–37 cm in length and 10–19 cm in width across the segments, with 8–12 segments per side that are narrowly oblong and 15–35 mm wide. The leaf apex is acute, and the upper surfaces are green and muricate, becoming aculeate in juveniles. In contrast, the lower surfaces are pale green, pubescent, muricate, and aculeate in juvenile plants. The leaf margins are irregularly dentate or lobed, with lobes ranging from acute to obtuse, and the petioles are 4–13 cm long, muricate, and aculeate in juvenile plants. The inflorescence comprises 5–8 flowers, clustered among the leaves and featuring muricate peduncles that are 20–60 mm long. The pedicels are 15–25 mm long, with linear bracts that are 15–30 mm long and 1–2 mm wide. The hypanthium is oblong to broadly ellipsoid, measuring 10–15 mm long and 5–10 mm wide. The calyx is 5-lobed with narrowly triangular lobes 8–24 mm long and 2–4 mm wide. The corolla is zygomorphic (bilaterally symmetric), either blackish purple or greenish white suffused with purple and 70–80 mm long by 7–10 mm wide. It is densely pubescent to muricate externally and glabrous within. The tube is arcuate, and the lobes spread, measuring ½–¾ the length of the tube. The stamens, five in number, are alternate with the corolla lobes and connate, with a glabrous staminal column and glabrous anthers. These anthers, which are dithecal and open by longitudinal slits, may all have apical tufts of white hairs or only the lower two. The fruit is a yellow ellipsoid berry 14–25 mm long, topped with persistent calyx lobes. The seeds are numerous, small, brown to black, smooth, and shiny, measuring 0.2–0.5(–2) mm long. They contain a straight, short, spatulate dicotyledonous embryo embedded in oily endosperm. It occurs in wet forest environments and the margins of subalpine forests, particularly on windward slopes, and is found at elevations ranging from 1,520-2,000 meters.