The genus Selenicereus belongs to the family Cactaceae and encompasses climbing and sprawling cacti native to tropical and subtropical regions of the Americas. Following a major taxonomic revision, Selenicereus now incorporates the former genus Hylocereus, making it one of the most economically significant genera in the family, principally on account of dragon fruit production.
Classification and nomenclature
The genus Selenicereus was described by Asa Gray in 1853. A comprehensive molecular phylogenetic study published in 2017 demonstrated that Hylocereus was nested within Selenicereus, and its synonymisation is now accepted by Plants of the World Online and most major botanical authorities. Common names include Queen of the Night for ornamental species, and dragon fruit or pitahaya for those cultivated for their edible fruits.
Morphological description
Habit and dimensions
Selenicereus are vigorous climbing or sprawling shrubs producing long, scandent stems that can reach 5–10 m or more. In their native habitat, plants ascend trees and rocky cliffs using aerial roots. In cultivation, they are typically trained on robust trellises or allowed to sprawl. The growth rate is rapid under warm, well-irrigated conditions.
Stems and areoles
Stems are elongated and ribbed, generally triangular or multi-winged in cross-section, and often bright green or glaucous. Ribs number 3–7 depending on species. Areoles bear small, inconspicuous spines 1–5 mm long, and many climbing species also produce aerial roots that assist in attachment to supports. The succulent stems are photosynthetically active.
Flowers
Flowers are among the largest in the Cactaceae, typically 20–35 cm in diameter, and open exclusively at night, lasting only a single evening. They are white, cream, or pale yellow, powerfully fragrant, and pollinated by nocturnal hawkmoths and bats. The long floral tube is covered in scales and hairs. Blooming often occurs synchronously across populations, maximising pollination success.
Fruits
Fruits are large, fleshy, ovoid to oblong berries, 6–15 cm long, bearing prominent scales on the skin. Flesh colour varies by species: white in Selenicereus undatus, red or pink in Selenicereus polyrhizus, and white with yellow skin in Selenicereus megalanthus. The flesh is sweet to mildly acidic, rich in water, and contains numerous small black seeds.
Distribution and habitat
Selenicereus is native to Mexico, Central America, the Caribbean, and northern South America, occupying tropical and subtropical forest edges, rocky slopes, and coastal scrublands. Through large-scale cultivation for fruit production, species such as S. undatus have been introduced worldwide and are now naturalised in parts of Asia, Australia, and the Mediterranean basin.
Main species
Selenicereus undatus, the white-fleshed dragon fruit, is the most widely cultivated species and a major commercial crop in Vietnam, China, Israel, and Latin America. Selenicereus polyrhizus produces red-fleshed fruit valued for its high antioxidant content. Selenicereus megalanthus, the yellow pitahaya, has yellow skin, white flesh, and is considered the sweetest of the three. Selenicereus grandiflorus, the original Queen of the Night, remains popular as an ornamental for its spectacular nocturnal blooms.
Cultivation
Climate and exposure
Selenicereus requires a warm, frost-free climate and full sun to partial shade. Optimal temperatures for fruit production lie between 18 and 38 °C. In temperate regions, plants must be grown in heated glasshouses. High light levels and long days promote flowering and fruiting. Substantial trellising or support structures are required for climbing species.
Substrate and watering
Well-draining sandy or loamy soil enriched with organic matter suits the genus. Regular watering during the growing season promotes vigorous growth and flowering; irrigation is reduced during cooler rest periods. Container cultivation requires large pots and regular fertilisation with a balanced NPK fertiliser supplemented with micronutrients during the fruiting period.
Cold hardiness
Most Selenicereus species are damaged at temperatures below 5 °C and killed by frost. Year-round glasshouse protection is necessary in the United Kingdom and northern Europe. In Mediterranean climates, established plants may tolerate brief, light frosts of short duration.
Conservation
Whilst many Selenicereus species are abundant in cultivation and the commercial dragon fruit industry, some wild populations face pressure from habitat clearance and over-collection. The entire genus is listed on CITES Appendix II, applying international trade controls to wild-sourced specimens. Commercially cultivated dragon fruit is produced from nursery-propagated material and is not subject to these restrictions.