Mexican lime Cactus Ferocactus pilosus is a simple or clumping barrel/column cactus with thick red spines. In habitat plants must be a great age, often forming into quite massive groups, with several subsidiary barrels growing from the main one, with deep green bodies densely covered with bright red spines up its entire length.
Most plants have bright red spines with bristle-like, white radials—a wonderful contrast, but in some populations the white bristles are occasionally absent. Such variation has led to establishment of several names for this species.
Stem: Columnar deep green up to 2,4(-3) m tall and 30 to 40 cm in diameter, with several subsidiary barrels growing from the main one. Ribs: 13-20, compressed, more or less undulate.
Areoles: Distant to closely set and almost contiguous in older specimens, circular. Radial spines: Sometime absent or usually reduced to long white or straw coloured hairs on the areoles that appears later with age.
Central spines: Several, subulate-acicular, stright or slightly curved, more or less flattened and angular at first bright red/purplish becoming dull yellow with age, but some populations also boast yellow-spined individuals, and the white bristles are occasionally absent.
Flowers: Yellow to red, about 2,5 cm long, scales on the ovary numerous, orbicular, imbricated, inner perianth segment oblanceolate, obtuse or apiculate. Fruits: Yellow, somewhat succulent, dehishing by basal pore, 3 to 4 cm long, crowned by persisting perianth.