Selenicereus
Selenicereus is a genus of climbing and sprawling epiphytic and lithophytic cacti native to the tropical Americas, prized by growers for their enormous, intensely fragrant flowers that open for a single night. Long, ribbed or angled stems clamber over rocks and up tree trunks by means of clinging aerial roots, and following a recent reshaping of the family the genus now also takes in the dragon fruits formerly placed in Hylocereus. Its members are widely grown as the moonlight cactus or night-blooming cereus.
Description
Selenicereus are climbing, trailing or scrambling cacti with slender to stout stems that can grow many metres long. Depending on the species the stems may be slim and few-ribbed, sharply three- or four-angled, or broad and winged, and they are typically bright to bluish green. All along the stems the plants produce aerial roots that grip bark, rock and other surfaces, letting the plant haul itself upward toward light while drawing moisture and humidity from the air. Spines are usually short, bristly and inconspicuous, though seedlings and juvenile growth can be more heavily armed.
The flowers are the genus's great attraction. They are among the largest of any cactus — funnel-shaped, often the size of a dinner plate — with slender outer segments framing a boss of creamy inner petals and a starburst of stamens. Most are pure white or cream, sometimes flushed with amber, pink or orange in the outer tepals, and heavily perfumed. Crucially they are nocturnal: buds swell over days, then open after dark for a single night, releasing scent to attract moths and (in some species) bats before closing forever by morning. The leathery-skinned, often spiny or scaly fruits are fleshy and, in the dragon-fruit species, large and edible.
Distribution and habitat
The genus ranges across the warm parts of the Americas — from Mexico and the Caribbean through Central America and into northern South America — with a few species reaching the southern United States. These are plants of humid tropical and subtropical forest, thornscrub and rocky slopes, where they grow as epiphytes anchored in the crotches of trees, as lithophytes sprawling over limestone and boulders, or scrambling through shrubs. In habitat they enjoy warmth, high humidity, dappled light beneath a canopy and the sharp drainage of loose bark, leaf litter and rock crevices rather than heavy ground soil.
Notable species
- Selenicereus grandiflorus — the classic queen of the night, celebrated for its huge, richly scented white flowers.
- Selenicereus undatus — the common white-fleshed dragon fruit (pitaya), formerly Hylocereus undatus, widely grown commercially for its fruit.
- Selenicereus anthonyanus — the fishbone or zig-zag cactus, with flat, deeply lobed stems popular as a hanging-basket houseplant.
- Selenicereus validus — a robust climber grown both as an ornamental and as a grafting stock.
- Selenicereus chrysocardium — the golden heart cactus, with broad, fern-like leafy stems.
Cultivation
Most Selenicereus are forgiving and vigorous, which makes them good beginner cacti so long as their tropical origins are respected. Unlike desert globulars they appreciate more warmth, more humidity and a little more water in growth, and they resent hard frost — keep them above about 5 °C and bring them in over winter in cool climates. Give bright light with protection from scorching midday sun; too much shade produces lush but weak, flower-shy growth, while gentle strong light encourages blooming.
Grow them in a chunky, free-draining, humus-enriched mix — a blend of bark, coir and mineral grit suits their epiphytic roots better than a pure sandy cactus mix. Water regularly through the warm months once the surface has dried, and ease off in winter to give a cooler, drier rest that helps trigger flowering. Because the stems are long and clambering, most growers train them up a moss pole, trellis or wire, or let them cascade from a hanging basket. See Watering, Repotting and Pests and diseases for general technique.
Propagation
Selenicereus are among the easiest cacti to propagate from cuttings. A length of stem cut and left to callus for a few days will root readily in a moist, airy medium, quickly making a new plant that is true to its parent — the standard way to increase named clones and the dragon-fruit cultivars. Seed is also viable and is used to raise new hybrids, though seedlings are slower to reach flowering size. Their vigour and thick, robust stems also make some species useful as grafting rootstock for slower or more delicate cacti. See Propagation — cuttings and Propagation — seed for full walkthroughs.
Hobby and cultivar notes
The genus spans two rather different corners of the hobby. On one side are the ornamental night-bloomers grown for spectacle — the queen of the night and the leafy fishbone cactus — treasured for foliage form and for the annual event of a plant-plate-sized flower opening after dark. On the other side is the booming world of dragon fruit cultivation, where the pitaya species (and their hybrids) have been selected into numerous named cultivars differing in flesh colour — white, red-magenta, pink — sweetness and self-fertility. Many dragon-fruit growers hand-pollinate the night flowers to guarantee fruit set, since some cultivars will not set fruit with their own pollen.
See also
- Cactaceae — the cactus family
- Epiphytic cacti
- Selenicereus grandiflorus · Selenicereus undatus · Selenicereus anthonyanus
- Grafting · Soil and potting mix · Watering · Propagation — cuttings · Propagation — seed