Cyanea macrostegia is a palm-like tree 1-7 m tall with unbranched stems. The simple, alternate leaves have oblanceolate to oblong or elliptic blades measuring 20–80 cm in length and 6.5–20 cm in width, with acute to obtuse, sometimes acuminate apices and cuneate, obtuse, or rounded bases. The leaf surfaces are glabrous or sparsely pubescent above and pubescent below, with callose-denticulate, sometimes erose-dentate margins. Petioles, ranging from 3 to 17 cm long, are often muricate, and the plant lacks stipules. The inflorescences bear 5–15 flowers clustered among the leaves, with peduncles 10–80 mm long and pedicels 10–25 mm. Flowers are bisexual (perfect), featuring a 5-lobed calyx with 6 to 55 mm long lobes. The corolla is zygomorphic (bilaterally symmetric), blackish purple outside and white or pale lilac inside, 60–80 mm long and 6–11 mm wide. It contains five stamens, with an inferior, 2-celled ovary. The fruit is a yellowish orange berry, obovoid or ellipsoid, 15–30 mm long, crowned by persistent calyx lobes. Seeds are numerous, small, brown to black, smooth, and shiny, measuring 0.6-0.7 mm in length. A straight, short, spatulate dicotyledonous embryo is embedded in an oily endosperm. It occurs in wet forests at elevations of 760–1,970 meters.