The genus Euphorbia includes many species classified as succulents. Succulence is a physiological adaptation, not a taxonomic group, which allows plants to store water in their fleshy stems, leaves, or roots to survive in arid climates. Euphorbia is one of the largest genera of flowering plants, containing over 2,000 species. The succulent forms are primarily native to the deserts and dry regions of Africa and Madagascar, though the genus has a nearly worldwide distribution.
Defining Succulence and the Euphorbia Family
Succulence describes any plant that has developed fleshy tissues to retain water, a response to environments experiencing extended periods of drought. This adaptation is a survival strategy that appears in many unrelated plant families. Euphorbia belongs to the Euphorbiaceae family, commonly known as the Spurge family.
The genus Euphorbia exhibits remarkable diversity, and not every species within it is succulent; for example, the Poinsettia (Euphorbia pulcherrima) is not considered a succulent. However, about 850 to 1,000 species, representing nearly half of the genus, are succulent, possessing thick, fleshy stems or roots. These water-storing species are commonly cultivated and often confused with other desert plants due to their similar appearance.
The Great Mimics: Distinguishing Euphorbia from Cacti
The confusion over whether Euphorbia is a succulent often stems from its striking resemblance to cacti, a phenomenon known as convergent evolution. Succulent Euphorbia species from the Old World (Africa) evolved independently to look like the cacti of the New World (the Americas) because they share similar arid environments. Despite the visual mimicry, three distinct morphological features easily separate them.
The most reliable differentiator is the areole, a specialized, cushion-like structure found exclusively on cacti, from which spines, flowers, and new branches emerge. Euphorbia plants completely lack this feature; their spines or thorns grow directly from the plant’s epidermis or stem. Furthermore, the sharp, defensive structures are botanically different: cactus spines are modified leaves, while many Euphorbia thorns are modified stipules or hardened flower stalks.
The arrangement of these defensive points is also telling, as Euphorbia thorns often appear in symmetrical pairs. In contrast, cactus spines typically emerge in clusters from the areole. The fundamental presence or absence of the areole is the definitive identification guide.
Unique Characteristics of the Genus
All members of the Euphorbia genus, whether succulent or not, share two defining internal characteristics. The first is the presence of a white, milky sap called latex, which exudes immediately when the plant tissue is broken or cut. This sticky fluid is a defense mechanism, deterring herbivores from feeding on the plant and sealing wounds to prevent water loss.
The second defining feature is the cyathium, a highly reduced and unique flower structure found nowhere else in the plant kingdom. The cyathium is a small, cup-shaped structure that groups together extremely simplified male and female flowers. Inside this cup, numerous male flowers are reduced to a single stamen, and a single female flower is reduced to a pistil on a stalk. What often appears to be a showy single flower is actually a specialized inflorescence, sometimes surrounded by brightly colored bracts that function to attract pollinators.
Practical Care and Handling
Caring for succulent Euphorbia species generally follows the protocols for most drought-tolerant plants. They require bright light, with many species thriving in full sun for at least six hours daily to maintain strong growth. A well-draining soil mix, typically a commercial cactus or succulent blend, is necessary to prevent root rot. Watering should be deep but infrequent, allowing the soil to dry out completely between applications, especially during winter.
The most crucial consideration for handling Euphorbia is the toxic latex, which can cause skin irritation, rashes, and blistering upon contact. If the sap enters the eyes, it can cause significant pain and temporary blindness.
Safety protocols must be observed when pruning, propagating, or repotting. Always wear protective gear, including gloves and eye protection, when handling the plant to avoid sap exposure. If skin contact occurs, wash the affected area immediately with soap and water. Keep these plants out of reach of children and pets, as the sap is poisonous.