Selenicereus undatus, the white-fleshed pitahaya, is a species of the genus Selenicereus (formerly Hylocereus) in the family Cactaceae and is the most cultivated species in the genus. It is used both as an ornamental vine and as a fruit crop – the pitahaya or dragon fruit. Like all true cacti, the genus originates in the Americas, S. undatus is originates from Mexico to Honduras; it may be a hybrid. It is most frequently attributed to the island of Martinique in the West Indies.

Description

Plant

Dragonfruit stems are scandent (climbing habit), creeping, sprawling or clambering, and branch profusely. There can be four to seven of them, between 5 and 10 mor longer, with joints from 30 to 120 cm or longer, and 10 to 12 cm thick; with generally three ribs; margins are corneous (horn-like) with age, and undulate. Areoles, that is, the small area bearing spines or hairs on a cactus, are 2 mm across with internodes 1 to 4 cm. Spines on the adult branches are 1 to 4 mm long, being acicular (needle-like) to almost conical, and grayish brown to black in colour and spreading, with a deep green epidermis.

Flowers

The scented, nocturnal flowers are 25 to 30 cm long, 15 to 17 cm wide with the pericarpel 2.5 to 5 cm long, about 2.5 cm thick, bracteoles ovate, acute, to 2.5 to less than 4 cm long; receptacle about 3 cm thick, bracteoles are linear-lanceolate, 3 to 8 cm long; outer tepals lanceolate-linear to linear, acuminate (tapering to a point), being 10 to 15 cm long, 10 to 15 mm wide and mucronate (ending in a short sharp point). Their colour is greenish-yellow or whitish, rarely rose-tinged; These outer tepals, or sepals are about 65 in number, and bring the flower to a total width of up to fourteen inches (35 centimeters). inner tepals are lanceolate (tapering to a point at the tip) to oblanceolate (i.e. more pointed at the base), up to 10 to 15 cm long about 40 mm wide at widest point, and mucronate, unbroken, sharp to acuminate (pointed), and white. Stamens 5 to 10 cm long, are declinate, inserted in one continuous zone from throat to 35 mm above the pericarpel and cream. The style (bearing the stigma) to 17, they are 5 to 24.5 cm long, stout, 6 to 8 mm thick, cream, and up to 26 stigma lobes, they can be whole or sometimes split at the top, cream, about 25 mm long. Nectar chambers are 30 mm long.

Fruit

The fruit is oblong to oval, 6 to 12 cm long, 4 to 9 cm thick, red with large bracteoles, with white, or more uncommonly, pink pulp and edible black seeds.

Habitat

Selenicereus undatus is lithophytic or hemiepiphytic. It is widely distributed through the tropics in cultivation. It is a sprawling or vining, terrestrial or epiphytic cactus. They climb by use of aerial roots and can reach a height of 10 meters (32.8 feet) or more growing on rocks and trees.

Systematics

This species is closely related to S. ocamponis and S. escuintlensis. Selenicereus undatus was described by (Haw.) Britton & Rose and published in Flora of Bermuda 256. 1918. In 2017, D. R. Hunt groups the genus Hylocereus within the genus Selenicereus. This has been supported by a phylogenetic analysis of the Hylocereeae tribe (Korotkova, et al., 2017), therefore this species is consigned under the name Selenicereus undatus

Taxonomy

The species's epithet undatus in Latin means "wavy" from unda "wave", referring to the wavy edges of its branches' ribs.

Common names