Copiapoa tenuissima
| Light | Very bright light; full sun with acclimatisation, some shade from the fiercest afternoon sun |
|---|---|
| Water | Very sparingly; allow to dry completely between waterings, keep dry through winter |
| Soil | Gritty, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; USDA zones 9b–11 |
| Propagation | Seed; offsets from clustered plants; grafting to speed slow seedlings |
| Toxicity | Non-toxic to cats and dogs |
Copiapoa tenuissima is a small, slow-growing cactus from the arid coast of northern Chile, distinguished by its dark, almost blackish-green body and fine, bristly spines. Often treated as a subspecies of Copiapoa humilis, it forms a low, flattened head that tends to cluster into tight groups with age, and produces bright yellow flowers. Its dark colouring and neat proportions make it a favourite in miniature and windowsill collections.
Description
Copiapoa tenuissima forms a small, more or less flattened globe, typically only a few centimetres across, on a stout tap root that often draws the body partly down into the soil. The skin is a distinctive dark greyish- to blackish-green — a colouring that intensifies with strong light and lean, dry conditions. The ribs are low and broken into gentle tubercles, each bearing a small areole with fine, short, bristly spines that are dark when young and weather to grey.
With age plants seldom stay solitary, instead offsetting to build low clusters of heads. The flowers are bright, glossy yellow, funnel-shaped, and borne from the woolly crown in the warmer months. As with the wider Copiapoa genus, the whole plant has an austere, sculptural look well suited to its harsh homeland.
Distribution and habitat
Like other members of the genus, C. tenuissima is native to the coastal desert of northern Chile — one of the driest regions on Earth. Plants of this group grow in mineral, stony ground under intense light and extreme aridity. Across the genus much of the available moisture comes not from rain but from the ocean fogs (the camanchaca) that roll in off the Pacific, though some populations grow in especially dry sites beyond the reach of the fog. In habitat the body frequently sits nearly flush with the surface among rock and grit.
Like the entire cactus family, Copiapoa is listed under CITES Appendix II, and wild Chilean populations are vulnerable to over-collection and habitat disturbance. Nursery-raised, seed-grown plants are the responsible and legal source; collecting from habitat is not.
Cultivation
Copiapoa tenuissima is a slow but rewarding plant that repays patience and restraint. Grow it in a very free-draining, mostly mineral mix in a deep pot that accommodates its tap root, and give it the brightest position you can — strong light is what keeps the body dark and the growth compact. Acclimatise gradually to full sun to avoid scorching.
Water is the main hazard. Water thoroughly only when the soil has dried out completely, and reduce sharply in the heat of high summer when the plant may rest; keep it bone dry and cool through winter. Overwatering, a heavy mix, or standing moisture around the crown quickly leads to rot. Because the species is naturally slow, some growers graft young seedlings to build size faster before growing them on their own roots. See Watering and Repotting for general technique.
Propagation
Seed is the primary method, though the fine seed and slow seedlings demand patience; sow on a warm, gritty surface kept humid until germination, then grow on hard and bright. Because established plants cluster, offsets can also be removed once they have their own roots or a firm base — see Propagation — offsets — and allowed to callus before potting, as described in Propagation — cuttings. Grafting onto a vigorous rootstock is a common way to speed up seedlings. See Propagation — seed for a full walkthrough.
Common problems
- Rot — the usual killer, almost always from overwatering, a slow-draining mix, or moisture trapped in the crown; the plant softens and discolours from the base.
- Etiolation and loss of colour — too little light makes the body pale green and swollen, losing both the dark tone and the flat, compact shape.
- Pests — mealybugs (white fluff in the areoles and around the root) and red spider mites (fine webbing, bronzed skin) are the common offenders; see Pests and diseases.
See also
- Copiapoa — the genus overview
- Copiapoa humilis — the species this taxon is often treated as a subspecies of
- Grafting · Soil and potting mix · Watering · Propagation — seed · Propagation — offsets