Acanthocereus
Acanthocereus is a genus of sprawling, angular-stemmed cacti native to the warmer parts of the Americas. Its name comes from the Greek akantha (thorn) and cereus (candle or wax taper), a nod to the spiny, columnar stems that scramble and lean rather than stand strictly upright. Most hobbyists first meet the genus through the triangle cactus (Acanthocereus tetragonus) and its popular dwarf, densely-branched form sold as Fairy Castle cactus.
Description
Acanthocereus are shrubby to clambering cacti with slender, sharply angled stems. In most species the young growth carries three to five prominent ribs or wings, giving the stem a distinctly triangular or star-shaped cross-section — the source of the "triangle cactus" name. Stems are green, often bluish when young, and armed at the areoles with clusters of stiff spines that can make a mature thicket genuinely impenetrable, hence the common name barbed-wire cactus.
Left to their own devices the stems sprawl, lean on surrounding vegetation, arch over and root where they touch the ground, forming tangled colonies. Flowers are large, funnel-shaped and nocturnal — typically white or cream, fragrant, and opening for a single night. Pollinated flowers give way to fleshy red fruits, which in some species are edible and locally gathered.
Distribution
The genus is spread through tropical and subtropical parts of the Americas, from Florida, Texas and Mexico south through Central America, the Caribbean and into northern South America. Typical habitat is low, hot scrubland, coastal thickets, hammocks and disturbed ground, often on sandy or limestone soils. Plants tolerate heat and periodic drought well but are firmly frost-sensitive.
Notable species
- Acanthocereus tetragonus — the triangle cactus, by far the most widely grown species and the source of the compact, heavily-branched Fairy Castle cultivar seen in garden centres. It is a broadly and variably circumscribed species; several names once applied to separate plants, among them A. horridus and A. subinermis, are now generally treated as synonyms of it.
Beyond the triangle cactus the genus takes in a number of other, mostly wild species of Mexico and Central America that are seldom seen in cultivation. The limits of the genus have been revised repeatedly, and a number of plants once placed here have been moved to or from related genera, so names in older literature and on nursery labels do not always agree.
Cultivation
Acanthocereus are undemanding, fast-growing cacti that reward warmth and light. Grow them in a very free-draining, mostly mineral mix and give bright light; the compact "Fairy Castle" form in particular stays denser and more colourful in strong light and etiolates into thin, stretched growth in shade.
Water generously through the warm growing season once the mix has dried, then ease off as temperatures fall — the stems are prone to rot if kept cold and wet. Keep plants above freezing; they are best treated as tender in any climate that sees frost, and are easily grown in pots that can move under cover for winter. The vigorous, sprawling species can outgrow a small pot quickly, so plan on periodic repotting and be mindful of the spines when handling. See Watering for general technique.
Hobby and cultivar notes
Within the hobby the genus is dominated by the triangle cactus and its forms. The Fairy Castle cactus — a dwarf, many-branched clone of A. tetragonus that builds up into a cluster of little turreted stems — is one of the most common beginner cacti sold, often alongside other easy columnar starters. Occasional crested and variegated sports appear; as with most such novelties these are less vigorous than the plain form and, if variegated, appreciate a touch more shade to avoid scorching the paler tissue.
The larger wild species are grown mainly by collectors and in frost-free gardens, where their scrambling habit and big night-flowers are the draw. All the common species propagate very easily from stem cuttings, which root readily once the cut end has callused.
See also
- Acanthocereus tetragonus — the triangle / Fairy Castle cactus
- Cactaceae — the cactus family
- Soil and potting mix · Watering · Propagation - cuttings · Repotting · Pests and diseases