Clermontia calophylla is a shrub or tree that can be terrestrial or epiphytic and ranges from 1.5 to 5 meters in height. The stems are repeatedly branched and spreading, light gray or light brown, and can be either glabrous or rarely pubescent. The apex of the stems has numerous helically arranged leaf scars, and the pith is solid with white, viscous latex. The leaves are simple and alternate. The blades are elliptic or broadly elliptic, measuring 12–19 cm long and 4–7 cm wide. The apex of the leaves can be acuminate, acute, or obtuse, while the base is cuneate. The upper surfaces of the leaves are glabrous, and the lower surfaces can be glabrous or pubescent. The blades are chartaceous and dull, with the upper and lower surfaces light green. The margins are callose-crenulate. The petioles are 3–7 cm long and pubescent. Stipules are absent. The flowers are in axillary, subumbellately racemose inflorescences with 2(–4) flowers and are pubescent. The peduncle is 1–1.7 cm long, spreading, and bibracteate at the middle or apex. The pedicels are 1–1.2 cm long, spreading, and bibracteolate at the middle. The flowers are bisexual, epigynous, zygomorphic (bilaterally symmetric), and resupinate, with protandry. The hypanthium is 1–1.7 cm long and 0.8–1.2 cm in diameter, obovoid, turbinate, or hemispheric, and can be glabrous or pubescent. The calyx is synsepalous with a tube that is adnate to the ovary, forming a hypanthium that can be hemispheric, obconic, obovoid, turbinate, or rarely oblong, and can be smooth or have ten longitudinal furrows, rarely muricate or with ten longitudinal ridges. The calyx lobes are five and valvate, either less than ½ as long as the corolla, distinct or rarely connate at the base, and persistent. The lobes can be triangular or deltate, rarely oblong or ovate, firm, green, or as long as the corolla (rarely only ⅔ as long), connate for 1/5–⅘ their length, deciduous, mimicking the corolla in shape, texture, and color. The perianth is 3.5–4.5 cm long, rotate, greenish externally, purple or dark purple within, and can be glabrous or pubescent. The tube is 1–1.8 cm long and 0.7–1 cm in diameter, erect or suberect. The lobes are five and valvate, 1.8–3.4 cm long and 1.2–2.5 mm wide, and recurved. There are five syngensious stamens, alternate with the corolla lobes, exserted, erect or suberect. The anthers are connate, dithecal, opening introrsely by longitudinal slits, dark purple, with the three dorsal ones being slightly longer than the two ventral ones, the latter having tufts of stiff white trichomes at the apex. The tube is 1–1.3 cm long and 3–4 mm in diameter, glabrous or sparsely pubescent. The filaments are 2.5–3.3 cm long, connate above, free from the corolla, purple or dark purple, and glabrous. The pollen is tricolporate, prolate, and ellipsoidal. The ovary is inferior, 2-carpellate, and 2-loculed with axile placentation and large placentae. The style is slender and terete, with a ring of stiff white hairs near the apex, and the stigma is 2-lobed, with the lobes appressed and non-receptive as the style grows through the anther tube, pushing out pollen, after which the stigmas spread and become receptive. The fruits are orange, subglobose berries 1.5–3 cm long and 1.5–3 cm in diameter. The pericarp is thick and leathery, and the placentae are juicy or spongy. The apex is truncate and crowned with a low circular rim and base of the style. The seeds are numerous, tiny, dark brown or black, minutely foveate-reticulate, shiny, with a straight, short to spatulate dicotyledonous embryo embedded in oily endosperm. It is found in montane rain forests at 885–1460 meters.