Espostoa
Espostoa is a genus of columnar cacti from the Andes of western South America, instantly recognisable by the dense coat of white wool and hair that cloaks their stems. Mature plants develop a distinctive lateral cephalium — a woolly, bristly flowering zone that forms down one side of the stem — from which the nocturnal flowers emerge. Their shaggy, silvery appearance has earned members of the genus common names such as Peruvian old man cactus and cotton ball cactus, and they are popular, forgiving subjects for the collector.
Description
Espostoa are slow-growing columnar cacti that are usually solitary when young and often branch from the base or lower stem with age, in time forming small candelabra-like clumps or short trees. The green stems are strongly ribbed and carry numerous fine spines, but their most striking feature is the covering of long white hairs and wool that hides the body to varying degrees — protecting the plant from intense Andean sun and cold.
As a stem matures it produces a cephalium along one flank: a band of dense wool and stiff bristles, sometimes flushed golden or reddish, from which flowering occurs. The flowers are typically funnel- to bell-shaped, whitish or pale, and open at night, pollinated in habitat by bats. They are followed by fleshy, often juicy fruits.
Distribution
The genus is native to the Andes of southern Ecuador and Peru, extending in a broad sense into Bolivia, where the plants grow on rocky slopes and in dry inter-Andean valleys at moderate to high elevations. These are montane, arid habitats with strong sun, sharp drainage and cool nights — conditions the wool coat is well suited to.
Notable species
- Espostoa lanata — the classic "Peruvian old man", freely white-woolly and the most widely grown species.
- Espostoa melanostele — densely hairy with a dark, contrasting cephalium at maturity.
- Espostoa nana — a smaller, especially shaggy species popular where space is limited.
- Espostoa senilis — cloaked in long, soft white hair over fine yellowish spines.
- Espostoa guentheri — a stouter species (sometimes segregated as Vatricania), notable for its prominent lateral cephalium.
Cultivation
Espostoa are among the more rewarding columnar cacti to grow. Give them the brightest position available — full sun encourages the densest, whitest wool, while too little light causes weak, sparsely haired growth. Plant in a very free-draining, mostly mineral mix and water generously during the warm growing season once the soil has dried, tapering off to keep the plant dry and cool through winter. Like most cacti they resent standing wet, and a cold, soggy winter is the usual cause of rot.
They tolerate more cold than many desert cacti thanks to their montane origins, but are safest kept above freezing. Repot growing plants every few years into a slightly larger, deep pot to accommodate the root system (see Repotting). General technique is covered in Watering and Pests and diseases.
Hobby and cultivar notes
Most plants in cultivation are grown from seed, which germinates readily on a warm, gritty surface; branches and offsets can also be rooted as cuttings once callused. Young Espostoa are frequently sold as woolly "old man" novelty plants, and some growers graft seedlings to speed them along, though the genus grows well enough on its own roots. Named cultivars are few — selection tends to favour individuals with the longest, whitest hair. Note that plants must reach considerable size and age before the cephalium and flowers appear, so most collection specimens are grown for their foliage-like wool rather than their bloom.
See also
- Grafting · Soil and potting mix · Watering · Repotting
- Propagation — seed · Propagation — cuttings · Pests and diseases