Garden expeditions to South America from the 1920s to the 1960s yielded many of the specimens in this collection, which includes desert plants from the southwestern United States, Mexico, and as far south as Chile and Argentina. Several beds feature plants from Mexico’s Baja California peninsula. The plants in this collection are some of the oldest in the Garden.

Deserts receive 25 centimeters (10 in) or less of rain each year. In some deserts rain might not occur for a year or more! Many desert plants cannot tolerate the Bay Area’s winter rains. Positioning the collection on a southwest-facing slope provides warmth and drainage critical to the survival of these plants.

Succulents are plants that store water. All cacti are succulents, but not all succulents are cacti. Habitat loss and over-collecting for the horticultural trade have endangered many cacti and succulents.

Plants from desert environments in different parts of the world may have similar structural forms, resulting from a process called convergent evolution. Compare the leaf rosettes of agaves with those of the southern African aloes.

Plants in the cactus family naturally occur only in North and South America, with the exception of one species of Rhipsalis in Africa. In the tropics some cacti are epiphytes, plants that grow on other plants.