Cyanea humboldtiana is a terrestrial shrub growing 1–2 meters tall, characterized by its woody, unbranched stems that are unarmed but can be muricate or aculeate. The leaves are simple and alternate, with obovate to broadly elliptic blades measuring 18–45 cm in length and 7–16 cm in width. The apex of the leaves ranges from acute to acuminate, with the upper surfaces glabrous and the lower surfaces pubescent. The leaf margins are callose-crenulate. Petioles are relatively short, measuring 3–4 cm. The inflorescences comprise 5–12 flowers, which are pendent and pubescent, with peduncles ranging from 80–250 mm long and pedicels 10–15 mm long. The hypanthium is oblong to obconical, 8–12 mm long, and pubescent. Flowers are bisexual (perfect), with a calyx that has five lobes, oblong and pubescent, ranging from 4–10 mm in length. The corolla exhibits a zygomorphic (bilaterally symmetric) structure, typically dark magenta or occasionally white, measuring 6-7.5 cm in height, pubescent, and features a suberect to strongly arcuate tube. The lobes of the corolla are connate and spread apart, and sometimes, all five lobes may curve downwards in the same plane. The five stamens are alternate with the corolla lobes, forming a glabrous staminal column. Anthers are pale, magenta, and glabrous, with the lower two having apical tufts of white hair. The ovary is inferior and 2-celled with axile placentation. The stigma is two-lobed and goes through a non-receptive phase before spreading apart to become receptive. The fruits are pale orangish-yellow berries, ellipsoid to obovoid, and 10–14 mm long. The seeds are numerous, small, pale brown to black, smooth, shiny, and contain a straight, short to spatulate dicotyledonous embryo within oily endosperm. It is found in wet forest habitats at elevations ranging from 300-915 meters.