While most people associate cacti with the Americas, these succulent plants are found beyond their traditional range. While the vast majority of cactus species are native to the Americas, one unique species is indigenous to Africa, and several others have been introduced and naturalized across the continent. This presence often leads to confusion, especially with native African plants that have evolved similar appearances.
The Sole Native Cactus
The only cactus species native to Africa is Rhipsalis baccifera, commonly known as the Mistletoe Cactus. This plant occurs naturally in tropical and subtropical regions of Central and South America, the Caribbean, and Florida, as well as in parts of Africa and Sri Lanka. Unlike typical desert cacti, Rhipsalis baccifera is an epiphyte, meaning it grows on other plants, often trees, without being parasitic. It features long, slender, pendulous stems that can resemble green spaghetti, and it lacks the prominent spines characteristic of many cacti.
Cacti Introduced to Africa
Beyond the single native species, numerous cactus varieties have been introduced to Africa, primarily from the Americas. The most widespread and recognizable of these are species belonging to the Opuntia genus, commonly known as prickly pears. These plants were initially brought to Africa for various purposes, including use as food, fodder for livestock, ornamental plants, or as living fences. For example, Opuntia ficus-indica was introduced to South Africa over 300 years ago, cultivated for its fruit and as a hedge plant. Today, these introduced cacti are prevalent in arid and semi-arid regions across the continent, often forming dense thickets.
Plants Often Mistaken for Cacti
Many plants in Africa, particularly those from the genus Euphorbia, are frequently mistaken for cacti due to their striking resemblance. This similarity is a classic example of convergent evolution, where unrelated species develop similar physical traits in response to comparable environmental pressures, such as arid climates. Both cacti and many succulent Euphorbia species have evolved fleshy stems for water storage and spines for protection against herbivores. However, a key botanical distinction lies in their structure: cacti possess areoles, specialized cushion-like structures from which spines, flowers, and new growth emerge, a feature absent in Euphorbia species.
Euphorbia plants typically produce a milky, often toxic, latex-like sap when cut, whereas most cacti do not. Their flower structures also differ significantly; cactus flowers are often large and showy, while Euphorbia flowers are usually small and less conspicuous. Common examples of African Euphorbia species that are often confused with cacti include Euphorbia trigona, known as the African milk tree, and Euphorbia ingens, which is sometimes called the Cowboy Cactus. These native African and Madagascan species thrive in dry environments, leading to their cactus-like forms.
Ecological Considerations of Introduced Cacti
The introduction of non-native cacti, particularly Opuntia species, has led to significant ecological challenges in many parts of Africa. These introduced species can become invasive, outcompeting native vegetation and reducing biodiversity. Their rapid spread often forms impenetrable thickets, which can degrade grazing lands and limit access to resources for both livestock and wildlife. In Kenya, for instance, Opuntia stricta has invaded thousands of hectares of rangelands, impacting animal herder livelihoods and potentially contributing to wildlife deaths.
To manage their spread, various strategies have been implemented, including biological control methods. In South Africa, the cochineal insect (Dactylopius opuntiae) and the cactus moth (Cactoblastis cactorum) have been successfully introduced to control prickly pear populations. These biological agents feed on the cacti, helping to reduce their density and impact on the ecosystem. While chemical and mechanical removal are also used, biological control is often considered a more cost-effective and sustainable long-term solution for widespread infestations.