Cacti are a unique group of plants, recognized for their succulent stems, often covered with spines, and vibrant flowers. They exhibit an array of forms and sizes, from small species to towering structures. Their ability to thrive in challenging environments prompts curiosity about their natural geographical origins.
The Americas: Cactus Homeland
The vast majority of the approximately 1,750 known cactus species are native to the Americas. Their natural range extends from Patagonia in southern South America north to parts of western Canada. This extensive distribution across North, Central, and South America highlights the continent as the primary center of cactus diversity. Mexico, in particular, boasts the greatest concentration and variety of native cacti species.
Cacti are nearly exclusive to the New World, with their evolution believed to have occurred after the ancient supercontinent Gondwana split into South America and Africa. This evolutionary history supports their presence almost exclusively in the Western Hemisphere, where diverse landscapes have allowed for an incredible array of species to adapt and flourish.
Diverse American Habitats
While often associated with hot, arid deserts, cacti exhibit remarkable adaptability, thriving in a variety of American habitats. Iconic desert regions like the Sonoran Desert in the southwestern United States and Mexico, and the Atacama Desert in Chile, are well-known for their abundant cactus populations. These environments feature species like the saguaro and organ pipe cacti, which have evolved to store water efficiently.
Beyond deserts, many cacti flourish in tropical and subtropical regions, including rainforests and cloud forests. These “jungle cacti,” such as some Epiphyllum (orchid cacti) and Hylocereus (dragon fruit) species, often grow as epiphytes, anchoring themselves to trees and absorbing moisture from the humid air and decaying organic matter. Cacti also inhabit high-altitude mountain environments, such as the Andes, where some species, like Oreocereus celsianus, are cold-tolerant.
The Old World Anomaly
A singular exception exists to the rule of cacti being exclusively native to the Americas: the genus Rhipsalis. Rhipsalis baccifera, often called the mistletoe cactus, is the only cactus species naturally found outside the Americas. Its native range extends to tropical Africa, Madagascar, and Sri Lanka.
The presence of Rhipsalis baccifera in the Old World has led to several theories regarding its dispersal. One hypothesis suggests migratory birds carried its seeds across the Atlantic Ocean, as Rhipsalis seeds are adapted for bird distribution. Another theory proposes that the species initially crossed the Atlantic on European ships trading between South America and Africa, with birds then spreading it more widely. Old World populations are polyploid and considered distinct subspecies, supporting an ancient dispersal event.