Myrtillocactus geometrizans f. cristata
Myrtillocactus geometrizans f. cristata is the crested (fasciated) form of the blue candle cactus, Myrtillocactus geometrizans. Instead of growing as upright, candelabra-like columns, the crested form's growing point elongates into a line, so the plant piles up in undulating, brain-like fans of the same waxy blue-green skin. Prized for its sculptural shape and its striking colour, it is one of the most familiar crested cacti in cultivation and a very popular ornamental and grafting subject, sold under names such as crested blue candle.
Crests of this kind arise from fasciation, a spontaneous change in which the normal single apical growing point becomes a growing line. Because the change is a growth abnormality rather than a stable genetic trait, a crested plant can occasionally throw a normal, upright ("reverting") stem, and growers usually cut these off to keep the fan form intact.
Description
The crested form shares the smooth, waxy, blue-grey to blue-green skin of the parent species, often with a fine pale bloom that rubs off to the touch. Rather than distinct columns, it forms broad, wavy crests and folds that thicken and lengthen with age, eventually building up mounded, coral- or fan-shaped masses. The ribs and low, dark, short-spined areoles of the ordinary plant are still present, but they are stretched and crowded along the crest line, giving the surface a rippled, closely furrowed texture.
Established, well-grown crests can flower with the small greenish-white blooms typical of the species, though flowering is less predictable on crested tissue than on normal columns.
Cultivation
Care follows that of the parent species, Myrtillocactus geometrizans — grow it in a fast-draining, mostly mineral mix, water thoroughly only once the soil has dried out, and keep it warm and dry through winter. Like the species, it tolerates only light, brief frost and is safest kept above freezing.
A few points are specific to the crest:
- Light and colour. Bright light brings out the best blue colouring and keeps the crest compact; in too much shade the plant grows softer, greener and can lose its dense fan shape. Introduce strong sun gradually to avoid scorching the exposed crest surface.
- Grafting. Crested Myrtillocactus is very often sold grafted onto a vigorous rootstock, which speeds growth and lifts the fan clear of the soil. M. geometrizans is itself widely used as a sturdy, long-lived stock for grafting other cacti, so growers encounter it on both sides of the graft.
- Watering and rot. The many folds of a crest trap water and debris, so water at the base and keep the crown dry; the crevices are a common starting point for rot if kept damp.
- Reverts. Watch for normal, round-tipped columnar growth pushing out of the fan and remove it early, or it will outgrow and disfigure the crest.
Propagation is vegetative: crested pieces can be taken as cuttings, calloused, and rooted, or grafted; seed does not come true to the crested form. See Repotting and Watering for general technique.
See also
- Myrtillocactus geometrizans — the parent species
- Myrtillocactus — the genus overview
- Grafting · Propagation — cuttings · Soil and potting mix · Watering