Pachycereus is a genus of 9–12 species of large cacti native to Mexico and just into southern Arizona, United States. They form large shrubs or small trees up to 15 m or more tall, with stout stems up to 1 m in diameter. Pachycereus comes from the ancient Greek pakhus meaning "thick" and the Latin cereus meaning "torch". P. pringlei is the tallest cactus species in the world, with a maximum recorded height of 19.2 m. Synonymy These genera have been brought into synonymy with Pachycereus: