Pilosocereus
Pilosocereus is a genus of tropical and subtropical columnar cacti native to the Americas, celebrated among growers for the intensely blue, waxy stems of several species and for the dense tufts of wool and long hairs that develop around their flowering zones. The name means "hairy Cereus", a nod to the woolly, bristly cephalium-like patches from which the night-opening flowers emerge.
Description
Pilosocereus are shrubby to tree-like cacti that branch from the base or form candelabra-like heads, with slender to stout ribbed stems that can reach several metres in the largest species. The ribs are usually well defined and carry closely spaced areoles bearing needle-like spines, though spine length and colour vary widely between species.
The most distinctive feature of the genus is the epidermis: many species are coated in a heavy blue-grey to almost powder-blue waxy bloom, one of the strongest blue tones found anywhere in the Cactaceae. As stems reach flowering size they develop a specialised lateral flowering zone, a woolly, often long-haired patch of dense areoles (a pseudocephalium) along one side of the upper stem. From this zone emerge the flowers — funnel-shaped, mostly white to pale pink or greenish, opening at night and typically bat- or moth-pollinated. The fruits are fleshy, often reddish or purple, and split to reveal juicy pulp and small black seeds.
Distribution
The genus is widespread through the warmer parts of the Americas, from Mexico, the Caribbean and Central America south into a major centre of diversity in eastern Brazil, with additional species across northern South America. Plants typically grow in hot, seasonally dry habitats — coastal scrub, rocky outcrops, dry forest and caatinga — often rooted in shallow, gritty or rocky soils in full sun.
Notable species
- Pilosocereus pachycladus — perhaps the bluest of all, a tall branching species from Brazil and a favourite ornamental.
- Pilosocereus azureus — another strikingly blue Brazilian columnar, widely grown (and often confused with, or treated as a form of, P. pachycladus).
- Pilosocereus leucocephalus — the "woolly torch" of Mexico and Central America, notable for its conspicuous white-haired flowering zone.
- Pilosocereus pentaedrophorus — a slender, elegant blue species from eastern Brazil.
- Pilosocereus gounellei — the "xique-xique" of the Brazilian caatinga, a robust, heavily spined species.
Cultivation
Most Pilosocereus are straightforward, fast-growing columnar cacti given warmth and light. Grow them in a free-draining, mostly mineral mix and give the brightest position available — strong light brings out the best blue colour and the densest waxy bloom, while too little light produces thin, green, etiolated growth. Water generously during the warm growing season once the soil has dried, then reduce sharply in winter and keep the plants drier and cooler at rest.
These are tender cacti with little frost tolerance; protect them from cold, wet winter conditions, which are the main cause of rot and scarring. Handle the stems as little as possible, since the beautiful waxy bloom is easily rubbed off and marks left by fingers or supports can be permanent. See Watering, Repotting and Pests and diseases for general technique.
Hobby and cultivar notes
Pilosocereus are prized in collections chiefly for their colour and stately form, and they make impressive specimen and landscape plants in frost-free climates. They are grown readily from seed, which germinates and grows quickly, and larger stems can also be rooted as cuttings — a useful way to reproduce a particularly blue clone, since seed-grown plants vary in colour intensity.
Because they are vigorous and undemanding, robust Pilosocereus stems are sometimes used as rootstock for grafting other cacti, though other columnar cacti are more commonly chosen for that purpose. Named cultivars are few compared with genera like Astrophytum; selection in the hobby tends to focus on the bluest, most heavily waxed individuals.
See also
- Cereus — a related columnar genus
- Grafting · Soil and potting mix · Watering · Propagation — seed · Propagation — cuttings