Pachycereus marginatusPachycereus marginatus Pachycereus marginatus, the Mexican fence post cactus, is a columnar cactus with dark green stems, strong vertical ribs and closely spaced areoles that form pale lines along the rib margins. Upright growth from the base gives the plant straight ribbed columns as stems thicken slowly over time. Short spines, firm stem tissue and the striped rib pattern create the species distinctive fence post look. Potted plants need strong