The simple answer is that while all cacti are succulents, not all succulents are cactus. But, like most things in life, it is can be considerably more complicated.
The cactus family Cactaceae, consisting of some 100 genera and about 1500 species subshrubs, shrubs and trees, native to the Americas. Other succulents are found worldwide, with tens of thousands of species in hundreds of genera scattered through dozens of botanical families.
Almost all cacti are leafless, their leaves having been replaced by spines, living in dry, barren habitats. But there are exceptions: several – the well-known Christmas cactus is one – use trees of the drier coastal tropical forests for support (technically they are epiphytic) and are spineless. Others conceal themselves among native grasses on the prairies as far north as Canada.
Some succulents also appear spiky, however, although at certain seasons they give themselves away by sprouting leaves. The so-called dragon bones ‘cactus’ is one such, botanically a Euphorbia, as is crown-of-thorns ‘cactus,’ both from the Old World, and often raised as houseplants.
Succulents derive their name from the Latin
succulentus, juice. Many are familiar are familiar garden plants of temperate regions. The many Sedum, stonecrops, will be recognized by even non-gardeners as will be the ubiquitous
Sempervivum, hens-and-chicks.
Many cacti have been transported, deliberately or accidentally into new areas. Indeed, the prickly pear cactus is so widely spread around the Mediterranean littoral that many are surprised to learn that this Opuntia is native to the Western Hemisphere. It has also been observed the subtropical gorges of Sichuan in the eastern Himalayas while in Australia it is classed as an obnoxious weed.
Humans, never quite content with what Mother Nature has to offer, have complicated things still further. Many cacti have been hybridized. Famed plant breeder Luther Burbank bred a spineless Opuntia for livestock forage. The gorgeous but confusingly called ‘orchid cactus’ are crosses of
Epiphyllyum, Rhipsalis and Nopalxochia, with more than 3,000 registered hybrids, were first developed by European breeders in the 19th century.
Alas, sad to say though, there is no truth to the claim that geneticists have succeeded in crossing citrus and cactus to produce spiked orange juice.
