Stetsonia
Stetsonia is a monotypic genus of cactus from the arid interior of central South America, containing a single species, Stetsonia coryne, the toothpick cactus. It is a large, tree-like, blue-green cactus of the Gran Chaco, where mature plants branch heavily into a broad candelabra crown carried on a short, woody trunk. The common name comes from its long, stiff, pale spines, which look strikingly like scattered toothpicks against the frosty stems.
Description
Stetsonia is a columnar, tree-forming cactus. From a distinct trunk it branches repeatedly into many upright, ribbed stems, building into a rounded crown that can reach several metres tall in habitat — one of the larger cacti of its region. The stems are a notably glaucous blue-green, divided into a modest number of broad, rounded ribs.
Along the ribs sit well-spaced areoles bearing straight, rigid spines that are whitish to pale grey with darker tips, the longest central spine standing out prominently. The flowers open at night: large, funnel-shaped and white, borne near the stem tips and followed by rounded fleshy fruit. The combination of blue-green stems, toothpick-like spination and eventual tree habit makes the genus hard to mistake.
Distribution
The genus is native to the Gran Chaco — the hot, semi-arid thornscrub plains spanning northern Argentina, western Paraguay, southern Bolivia and adjacent Brazil. There it grows in dry forest and open scrub on sandy or stony ground, often as a conspicuous emergent among the low, spiny vegetation. Populations experience strong summer heat and rainfall with a pronounced dry season, conditions that inform how the plant is best grown in cultivation.
Notable species
As a monotypic genus, Stetsonia contains only one accepted species:
- Stetsonia coryne — the toothpick cactus, the sole species and the source of all the genus's ornamental interest.
Cultivation
Stetsonia is a robust, undemanding grower for a large-growing cactus, valued for its blue coloration and bold spines even when young. Give it strong, direct light to keep the stems compact and well-coloured, and a very free-draining, mostly mineral mix. Water generously through the warm growing season once the soil has dried, then keep it dry and cool in winter, when the plant rests. It tolerates considerable heat and drought but resents cold, wet soil, which is the usual cause of rot.
Young plants are happy in containers for years, growing steadily; only in the ground in a suitably warm, frost-free climate will a plant approach its full tree-like stature. See Watering and Repotting for general technique, and Pests and diseases for the usual glasshouse pests such as mealybugs and scale.
In cultivation
The genus is grown mainly as an ornamental for its frosty blue stems and dramatic spination, and it makes a striking specimen or landscape plant in dry gardens. Being monotypic, Stetsonia has no named horticultural forms of any significance, and plants in the trade are simply grown from seed.
Propagation
Propagation is chiefly by seed, which germinates readily under warm, humid conditions on a mineral surface. Cuttings of the branching stems can also be rooted after the cut surface has calloused; see Propagation — cuttings.
See also
- Stetsonia coryne — the toothpick cactus, the only species
- Grafting · Soil and potting mix · Watering · Propagation — seed · Propagation — cuttings