Espostoa guentheri
| Light | Bright light to full sun once established |
|---|---|
| Water | Moderate in the growing season; keep dry and cool in winter |
| Soil | Fast-draining, gritty mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; roughly USDA zones 9b–11 |
| Propagation | Seed; occasionally cuttings |
| Toxicity | Non-toxic to cats and dogs |
Espostoa guentheri, also treated as Vatricania guentheri, is a columnar cactus native to the seasonally dry country of eastern Bolivia. It is best known for the striking, bristly cephalium that develops down one side of a flowering stem — a dense band of wool and stiff bristles from which the flowers emerge — a feature that once set it apart in its own genus, Vatricania. Although horticulture still widely files the plant under Espostoa, molecular studies support keeping it distinct, and Vatricania guentheri is the name currently accepted by Kew's Plants of the World Online; the placement remains unsettled.
Description
Espostoa guentheri is a stout, erect columnar cactus that branches from near the base with age to form a shrubby clump, with pale green stems reaching up to about 2–3 m tall and roughly 10 cm thick, clothed in numerous (about 27) low, barely tuberculate ribs. The areoles carry fine, pale to straw-coloured spines and a covering of hair that softens the outline of the stem, in the manner typical of the genus.
The species' signature feature is its lateral cephalium — a flowering zone that forms as a wide band of dense wool and long, coarse bristles running down one flank of a mature stem. In this species the wool and bristles are notably stiff and take on a reddish-brown to rust tint, giving the cephalium a shaggy, foxtail-like appearance. Nocturnal, funnel- to bell-shaped, cream to yellowish-white flowers push out through this woolly band, followed by fleshy fruits. The unusual, superficial nature of the cephalium is what historically justified separating it as Vatricania.
Distribution and habitat
The species is endemic to Bolivia, where it grows in the hot, seasonally dry valleys and hillsides of the country's east, at roughly 800–1,300 m. There it roots in stony, well-drained ground among xerophytic dry-forest scrub, exposed to strong sun and marked wet and dry seasons. As with the whole cactus family, this species is listed under CITES Appendix II, but nursery-propagated plants are legal to own and trade; wild collection is not.
Cultivation
Espostoa guentheri is a rewarding grower for anyone with the space for a columnar cactus. Plant it in a very free-draining, mostly mineral mix and give it bright light, working up to full sun once the plant is established, as strong light keeps growth compact and encourages the hair and eventual cephalium to develop well.
Water moderately through the warm growing season, always letting the mix dry out before watering again, then keep the plant dry and cool over winter to prevent rot — the most common cause of loss with columnar cacti. Protect from frost; although mature plants tolerate a brief touch of cold when dry, a minimum comfortably above freezing is safest. The cephalium only forms on mature stems, so patience is needed before you see the species at its most distinctive. See Watering and Repotting for general technique.
Propagation
Seed is the usual and most reliable method: sow on a warm, mineral surface kept humid until germination, then grow the seedlings on hard in bright light. Established clumps can also be increased from stem cuttings, which should be left to callus for a week or more before being set in a dry, gritty mix to root. See Propagation — seed for a full walkthrough.
Common problems
- Rot — almost always from overwatering, a slow-draining mix, or cold wet conditions in winter; the stem softens and discolours, often from the base.
- Etiolation — too little light produces pale, thin, drawn-up growth that never develops good hair or a proper cephalium.
- Pests — mealybugs (white fluff in the areoles and among the wool) and red spider mites (fine webbing, bronzed skin) are the usual offenders. See Pests and diseases.
See also
- Espostoa — the genus overview
- Cephalium
- Soil and potting mix · Watering · Propagation — seed · Propagation — cuttings · Repotting