The genus Myrtillocactus belongs to the family Cactaceae and contains only four species of tree-like columnar cacti native to Mexico and Guatemala. Known for their candelabra-branching habit, glaucous blue-green stems, and edible fruits, these plants are ecologically and economically important in their native region and are widely used as grafting rootstock in commercial cactus cultivation.
Classification and nomenclature
Myrtillocactus was described by Friedrich Vaupel in 1897; the name derives from the Latin myrtillus (bilberry or whortleberry), alluding to the blueberry-like fruits, combined with cactus. The genus belongs to subfamily Cactoideae, tribe Pachycereeae, and is most closely related to Stenocereus and Polaskia. Only four species are accepted: M. geometrizans, M. cochal, M. eichlamii, and M. schenckii.
Morphological description
Habit and dimensions
Myrtillocactus species are tree-like, branching freely from a short, distinct trunk to form a broad candelabra crown. Mature specimens of M. geometrizans can reach 4–5 m in height and comparable width, creating an impressive landscape plant. The clear division between trunk and canopy distinguishes Myrtillocactus from many other branching columnar cacti.
Stems and areoles
Stems are cylindrical, 6–12 cm in diameter, and bear 4–8 ribs depending on the species. The epidermis is glaucous, typically blue-green to grey-green, with a waxy bloom. Areoles are spaced well apart along the ribs and carry a central spine that may be dagger-like and several cm long, along with shorter radial spines. Multiple flowers can arise from a single areole — an unusual feature among cacti.
Flowers
Flowers are small (2–3 cm), cream to greenish-white, and diurnal. They are produced in clusters of up to 9 per areole in M. geometrizans, which is exceptional within the family. The flowers are open and star-shaped, produced in spring, and are pollinated by insects and small birds. Their modest size belies the abundance in which they appear on large specimens.
Fruits
Fruits are small, globose, 1–2 cm in diameter, and ripen from green through red to dark purple or bluish-black — strikingly similar to blueberries or bilberries, hence the genus name and the common name “garambullos” for M. geometrizans. The fruits are sweet, edible, and widely eaten fresh or dried in rural Mexico. They are also commercially harvested in some areas.
Distribution and habitat
Myrtillocactus geometrizans, the most widespread species, dominates the semi-arid scrublands of the Mexican Plateau (Altiplano), particularly in the states of Hidalgo, Querétaro, San Luis Potosí, and Guanajuato, where it forms dense stands called “cardonal”. M. cochal is found in Baja California, M. eichlamii in Guatemala, and M. schenckii in Oaxaca. All species grow in well-drained soils in warm, seasonally dry climates at altitudes of 500–2,200 m.
Main species
Myrtillocactus geometrizans (Mart. ex Pfeiff.) Console is by far the most important species horticulturally and economically. In Mexico it serves as the dominant grafting rootstock for slow-growing or difficult cacti, valued for its vigorous growth, disease resistance, and wide compatibility. Cultivated forms include the popular “breast cactus” or “titty cactus” (M. geometrizans f. monstrosa), which develops abnormally swollen ribs, and the rare crested form.
Cultivation
Climate and exposure
Full sun and warm temperatures are required for healthy growth. Myrtillocactus grows vigorously during the warm season and is well adapted to the alternation of wet summers and dry winters. In temperate climates, plants grow well outdoors in summer but require overwintering under glass or indoors.
Substrate and watering
A mineral, fast-draining substrate is ideal. Water generously during the growing season and allow thorough drying between waterings. In winter, keep nearly dry. Myrtillocactus geometrizans is particularly valued as a grafting rootstock because of its reliable vigour and ease of cultivation; grafted plants grow considerably faster than self-rooted specimens.
Cold hardiness
Mature, well-established plants of M. geometrizans can tolerate brief frosts to around −5 °C if kept dry — a useful level of cold tolerance for Mediterranean gardens. Young plants and grafted specimens are considerably more vulnerable and should be protected from any frost.
Conservation
Myrtillocactus geometrizans remains abundant within its natural range and is not currently threatened. Its value as a food plant and grafting rootstock has, if anything, encouraged its preservation by local communities. However, the rarer species such as M. eichlamii and M. schenckii have more restricted ranges and may face localised threats from habitat clearance. The genus is regulated under CITES.