Hylocereus megalanthus is a terrestrial or epiphytic, creeping, climbing, or hanging, richly branched cactus with succulent, winged shoots up to 6 m long that attach to the substrate with aerial roots.
The flowers form on green, rounded flower shoots, which have fleshy, protruding scales and surround the ovary. The flowers only open at night and are pollinated by bats.
The fruits (known as pitaya) are thornless, fleshy, round or oval berries with a ripe pink-red skin featuring triangular scales up to 8 cm long. The pitayas grow up to 20 cm in size. The skin is 1 cm thick and encloses a fruit cavity filled with translucent white, juicy pulp containing many black seeds up to 3 mm in size.