Etymology -The name refers to the fruits which resemble those of the Bilberry (Vaccinium myrtillus).
There are four species of Myrtillocactus which are recognized and unlike most other cactus genera, the taxonomy of Myrtillocactus is quite settled and universally accepted.
The four species are all similar in that they are tree-like, much-branching plants with few (4-8) prominent ribs. Typically the ribs features a single, thick, long central spine and only a few thick, short radial spines or the areoles may be spineless. Flowers are quite small at less than an inch (2.5cm) and have short floral tubes which keep the flowers fairly tight to the stems. An unusual feature of Myrtillocactus is that the areoles may produce multiple flowers. The flowers are a greenish-white color, waxy and somewhat translucent. Large sections of the ribs will feature flowers all at once and later give rise to blue-berry-like fruits which are very tasty and have been used by native people of Mexico for centuries and are still harvested today. The fruit often goes by the common name "Garambullo" in the local markets. The fruit has also been likened to Bilberry (Vaccinium myrtillus) and true Myrtle (Myrtus communis).
The species, M. geometrizans is one of the most common plants in cultivation. While potted plants are highly unlikely to ever be grown large enough to produce flowers and fruits, those in more temperate climates can plant it as a landscape plant where it will grow very quickly. The other three species are very rare in cultivation.
In the wild, the Myrtillocactus species are widespread in Mexico including the Baja California peninsula.