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Pilosocereus pachycladus F. Ritter is a native cactus which is grown in the semi-arid area of northeastern Brazil. The specimens have an ornamental value, yet studies on their anatomy are scarce. The root anatomy of P. pachycladus was studied in order to understand better the adaptation mechanisms. Specimens were collected in Areial, Arara and Boa Vista, State of Paraiba. Cross sections of roots were clarified with sodium hypochlorite (50%), stained with safranin and blue astra and examined under light microscopy. In general, the secondary structure of the roots was similar for the genotypes collected at the three sites. We observed the replacement of the epidermis by periderm, a cortex with few layers of parenchyma, collateral vascular bundles and fibers located in the parenchyma rays between beams. Druses were present in the cortical region. These were observed in higher numbers in roots collected in Areial and less frequently in roots from plants growing in Boa Vista. The presence of crystals indicates the adaptive capacity towards the xeric conditions, as a higher amount of druses was observed in specimens growing in warmer climate. This study contributes to the establishment of anatomical parameters, contributing to the taxonomy of the species.