Senita Cactus – Desert Botanical Garden, Papago Park, Phoenix, Arizona

Since it cannot tolerate even the slightest frost, the senita (pachycereus schottii – synonyms include Pilocereus schottii and Lophocereus schottii) is by far the rarest of Arizona’s big three cacti (the others being saguaro and organ pipe). The senita is found only in a small narrow band along the southern edge of Organ Pipe Cactus National Monument. The best place to see them is at Senita Basin, on the sheltered, south-facing slopes of the Puerto Blanco Mountains. Like the organ pipe, the senita is much more widespread in Mexico, where frosts never occur. Even in the national monument, many specimens show damage as a result of cold weather spells.

Pachycereus schottii forms extensive clusters, of a hundred or more stems, up to 20 feet tall, branching from the base – like the organ pipe, but easily distinguished from the organ pipe as the senita has fewer ribs (five or six), as well as shorter, lighter and more widely separated spines, and because the top portion of each stem is covered by dark, hairy tufts, after which the plant is named. Senita (‘old’ in Spanish) comes from the resemblance to an old man’s beard. The short spines allow the bright yellowish green stem to be prominently visible. Flowers are borne along the stems, unlike the saguaro and organ pipe which bloom from the tips.