Myrtillocactus geometrizans is a large shrubby cactus growing to 4–5 m tall, with candelabra-like branching on mature plants. The individual stems are 6–10 cm diameter, with five (occasionally six) ribs, with areoles spaced 1.5–3 cm apart. The flowers are creamy white, 2–2.5 cm diameter. The fruit is an edible dark purple berry 1–2 cm diameter, superficially resembling Vaccinium myrtillus (bilberry or whortleberry) fruit; both the scientific and English names derive from this resemblance.