Columnar Cacti is an ongoing educational website created through a collaboration between cactus enthusiasts Tony Mace of Ansty, West Sussex, and Bob Ressler of Stockton, California. Hosted as part of the Cactus Mall, the site focuses on giant, tree-like cacti, a group the contributors say receives less attention than smaller globular varieties despite being widely cultivated and sold through nurseries.

The website provides information on numerous columnar cactus genera, with existing in-depth coverage of Browningia and Espostoa. Its planned and developing resources include photographs of seedlings and mature plants, examples from cultivation and the wild, original botanical descriptions, distribution maps, and references to articles. The project also aims to preserve Bob Ressler’s photopoint galleries and digitize Tony Mace’s ceroid slide collection. Additional contributions include an article on ceroid cacti in Michoacán by Arturo Anaya and material on xMyrtgerocactus. Written from an amateur enthusiast’s perspective, Columnar Cacti welcomes corrections and contributions to help expand and improve its reference material.