Description from Flora of China
Cereus undatus Haworth, Philos. Mag. Ann. Chem. 7: 110. 1830.
Plants clambering or sprawling. Stems deep green, 3-15 m. Joints 20-50 × 3-8(-12) cm, winged or angled, margins of wings or angles coarsely crenate, horny. Areoles 3-6 cm apart, 2-5 mm in diam. Spines 1-3(-6) per areole, spreading in various directions, gray-brown, conic to subulate, 2-5(-10) mm. Flowers 25-30 × 15-34 cm. Receptacle tube funnelform. Sepaloids with greenish midrib and mostly white margin, lanceolate-linear to linear, 10-15 × 1-1.5 cm, margin entire, apex acuminate, reflexed. Petaloids erect to spreading, white, narrowly oblanceolate, margin entire or erose. Filaments cream, 5-7.5 cm; anthers linear, ca. 4.5 mm. Style cream, 14-20 cm, stout; stigmas 20-24, exserted, 2-2.3 mm, slender. Fruit red, globose to ellipsoid, 7-12.5 × 6-12 cm, with numerous triangular scales, umbilicus small; pulp white. Seeds obovate, ca. 2 × 1 mm. Fl. July-Dec.
This species was first introduced to China in 1645. It is usually cultivated as a hedge, or for its edible fruit. The flower is often eaten in a vegetable soup in S Guangdong.
Trees, rocks, maritime scrub; sea level to 300 m. S Fujian, S Guangdong, SW Guangxi, Hainan, Taiwan [perhaps native to Mexico and Central America; widely introduced and escaped in tropical Asia, E Australia, and South America].