They look alike, but they are not the same
At first glance, it is easy to confuse them: they have thick green stems, spines, and an appearance clearly adapted to the driest environments. However, despite their striking resemblance, they belong to different botanical families and originate from different continents.
Cacti (family Cactaceae) are native to the Americas, whereas most succulent spurges (genus Euphorbia) originate from Africa and Madagascar. Despite this geographical and evolutionary separation, many species have developed remarkably similar forms.
Evolutionary convergence: the same response to the same challenge
This phenomenon is known as evolutionary convergence: different organisms that, by living under similar environmental conditions, develop similar adaptations. Although the term “evolutionary convergence” came later, Charles Darwin had already described in On the Origin of Species (1859) how natural selection could lead different species to develop similar characteristics in response to comparable environmental challenges.
In environments with scarce water, high temperatures and long periods of drought, both cacti and euphorbias have evolved stems capable of storing water, spines that protect them from herbivores and help reduce the plant’s exposure to heat, and compact forms that allow them to withstand extreme conditions more effectively.
How can we tell them apart?
There are several features that make it possible to distinguish them. Cacti have areoles, small specialised structures from which the spines, flowers and new shoots emerge. Their flowers are usually large and showy, an adaptation that helps attract pollinators.
Euphorbias, on the other hand, do not have areoles. Another distinctive feature is that, when a stem is broken, they usually release a white latex, a substance that acts as a defence mechanism against herbivores and can be irritating to the skin and eyes.
A remarkable example of evolution’s ingenuity
Cacti and euphorbias remind us that two plants can become extraordinarily similar without sharing a close evolutionary origin. Faced with the same environmental challenge, evolution is capable of finding remarkably similar solutions, making these species one of the best-known examples of evolutionary convergence.
