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Why do cacti and euphorbias have similar forms despite belonging to unrelated plant families?

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Zenaida macroura: mouring doves — ecology Mourning doves (*Zenaida macroura*) on their nest protected within the prickly branches of a cactus in the Sonoran Desert, Arizona, U.S.

Cacti and euphorbias exhibit similar forms because they have undergone convergent evolution, a process where unrelated organisms independently evolve similar traits as adaptations to comparable environmental challenges.123

Although they belong to distinct plant families, both groups have adapted to arid, desert conditions by becoming succulents—plants with thick, fleshy tissues designed for water storage. To survive in these dry environments, both have developed analogous features, such as spiny, water-storing stems, which help minimize water loss and protect against herbivores.1456

These shared characteristics are not the result of common ancestry but are instead the product of natural selection favoring similar morphological and physiological solutions to the same ecological pressures. While they may look alike, they remain biologically distinct; for instance, unlike cacti, many succulent euphorbias contain a milky, often poisonous sap.1367