Leuchtenbergia principis
| Light | Very bright light to full sun once established |
|---|---|
| Water | Moderate in growth; keep dry and cool in winter |
| Soil | Deep, very free-draining mineral mix in a tall pot |
| Temperature | Keep above freezing; roughly USDA zones 9–11 |
| Propagation | Seed (primary); occasionally offsets or grafting |
| Toxicity | Not known to be toxic |
Leuchtenbergia principis, the agave cactus or prism cactus, is a striking, slow-growing cactus from the deserts of north and central Mexico and the only species in the genus Leuchtenbergia. It is unmistakable: a stout, tuber-like base and taproot give rise to long, slender, three-sided tubercles up to about 12 cm long, each tipped with an areole bearing flexible, papery spines, and in summer the plant produces large, fragrant, silky yellow flowers. The tubercles and their soft spines make the plant look far more like an Agave than a typical cactus, which is the source of its common name.
Description
Leuchtenbergia principis grows from a thick, fleshy taproot and a woody, tuberous stem base that stores water and anchors the plant deep in dry ground. From this base spiral the plant's defining feature: long, narrow, sharply three-angled tubercles, greyish-green, each ending in a raised areole. Rather than rigid spines, the areoles produce long, thin, flexible spines with a papery, straw-like texture that bend easily and do little to defend the plant — an unusual trait among cacti.
As older tubercles at the base dry and shrivel, the woody stem is slowly revealed beneath, and mature plants may take on a short, columnar look topped by the living crown of tubercles. Flowers open from the areoles near the tips of young tubercles in summer, are large and glossy yellow, sweetly scented, and last several days. They are followed by smooth greenish fruit containing black seed.
Distribution and habitat
The species is native to the Chihuahuan Desert region of north and central Mexico, across states including Coahuila, Nuevo León, San Luis Potosí and Hidalgo. It grows on limestone hills and in dry scrub and grassland, often rooting in gritty or rocky soils among low vegetation. The deep taproot lets it survive long droughts and pull the vulnerable crown low against the ground, where surrounding shrubs and grasses offer some shade and protection.
Cultivation
Leuchtenbergia principis is slow but not difficult, and rewards patience. The key is drainage and root room: because of its long taproot, it does best in a deep pot filled with a very free-draining, mostly mineral mix. Give it strong light — bright conditions and, once acclimatised, a good amount of direct sun keep the tubercles compact and the plant in character.
Water moderately through the warm growing season, always allowing the mix to dry out between waterings, then keep the plant dry and cool over winter to prevent rot and encourage flowering. The fleshy taproot is prone to rot if kept wet, so err on the side of underwatering. See Watering and Repotting for general technique; when potting on, handle the brittle taproot carefully.
Propagation
Seed is the usual and most reliable method. Fresh seed germinates well on a warm, mineral surface kept lightly humid, though seedlings are slow to size up. Mature plants sometimes produce offsets from the base, which can be removed and rooted, and — as with many slow cacti — seedlings are occasionally grafted onto a vigorous rootstock to speed early growth before being grown on their own roots. See Propagation — seed and Propagation — offsets for full walkthroughs.
Cultivars
Selection in Leuchtenbergia is limited compared with many popular cacti. The best-known deviation from the ordinary plant is a crested (f. cristata) form, in which the growing point fans into a contorted crest of fused tubercles; crested plants are prized by collectors and are usually maintained by grafting. Intergeneric hybrids with the related genus Ferocactus, known as the nothogenus ×Ferobergia, have also been produced by specialists.
Common problems
- Rot — the most common cause of loss, almost always from overwatering or a slow-draining mix; the taproot and base soften and discolour.
- Etiolation — too little light produces weak, over-long, pale tubercles and a floppy, stretched habit.
- Pests — mealybugs (white fluff in the areoles and around the roots) and red spider mites (fine webbing, bronzed skin) are the usual offenders. See Pests and diseases.
See also
- Leuchtenbergia — the genus overview
- Grafting · Soil and potting mix · Watering · Propagation — seed · Propagation — offsets · Repotting