While it might seem straightforward, the answer is more nuanced than a simple yes or no. True cacti, belonging to the family Cactaceae, have a specific evolutionary history and geographic origin that largely excludes Africa. Understanding this distinction involves exploring where cacti truly come from, how they came to be present in Africa, and the native African plants that frequently resemble them.
Cacti’s Native Origins
True cactus species (family Cactaceae) are indigenous to the Americas. Their natural range extends from western Canada down to Patagonia in South America, encompassing diverse environments from deserts to tropical forests. This family comprises about 127 genera and around 1,750 known species, all originating from the New World.
Cacti have developed adaptations to thrive in arid and semi-arid conditions. Their stems are often thick and fleshy, designed to store significant amounts of water, and they conduct photosynthesis through these stems rather than traditional leaves. Spines, which are modified leaves, help reduce water loss by limiting airflow near the plant surface and deterring herbivores.
The evolutionary timeline of cacti suggests they appeared between 30 and 35 million years ago, likely in southern South America, well after the ancient supercontinent Gondwana split into South America and Africa. This geological separation explains why cacti are predominantly found in the Americas. However, there is one notable exception to this rule: Rhipsalis baccifera, often called mistletoe cactus. This epiphytic species, which grows on trees, is found naturally in parts of Africa, Sri Lanka, and Madagascar, making it the only cactus species indigenous outside the Americas.
How Cacti Arrived in Africa
Despite their American origins, cacti are now commonly seen in various parts of Africa due to human introduction over centuries. The primary method of their arrival was through colonization, trade routes, and subsequent agricultural practices.
A key example is the prickly pear (Opuntia ficus-indica), introduced to South Africa over 300 years ago. This species was initially valued for its edible fruit, which can be consumed fresh or processed into jams and other products. It also served as a source of fodder for livestock, particularly during drought conditions, and was used as ornamental plants or even as living fences.
Its ability to reproduce easily from detached pads and its drought resistance allowed it to naturalize rapidly. In certain African ecosystems, the prickly pear and other introduced Opuntia species became invasive, forming dense thickets that displaced native vegetation. This has led to significant ecological challenges in regions like the Eastern Cape of South Africa, where they are now considered alien species.
African Succulents That Resemble Cacti
The visual similarity between some native African succulents and true cacti often leads to confusion about cacti’s presence on the continent. This resemblance is a result of convergent evolution, where unrelated species develop similar traits because they adapt to similar environmental pressures, such as arid conditions.
The genus Euphorbia (family Euphorbiaceae) contains numerous species that mimic cacti. These succulent Euphorbia species are diverse and abundant in southern and eastern Africa and Madagascar. They often feature thick, angled, spiny stems, leading people to mistake them for cacti.
There are distinguishing characteristics that differentiate Euphorbia from true cacti. A primary difference is the presence of milky, latex-like sap in Euphorbia species, which is typically absent in cacti. This sap can be irritating and even toxic upon contact. Another key identifier is the unique floral structure of Euphorbia, where individual flowers are tiny and grouped into a specialized structure called a cyathium, unlike the often large and showy flowers of cacti. Furthermore, true cacti possess areoles—small, cushion-like structures from which spines and flowers emerge—a feature not found in Euphorbia.