What is the classification for a cactus?

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Carl von Linne, also known as Linnaeus, devised a system of categorizing plants and animals into specific groups. Large groups are known as genera (genus is the singular form); more specifically, smaller ones are called species. Together these botanical breakdowns help us identify plants according to families – all of which share certain characteristics.

To some people, calling plants by their botanical name seems unnecessary. However, unlike common names that may mean one thing to a cactus grower in Phoenix and something completely different to a collector in New York, botanical names are reliably accurate.

One of the most fascinating things about plant nomenclature is the reasoning behind it: plants are usually given names for a specific reason. It may be to describe their appearance, growth habitat, where they were first discovered or who discovered them.

Look at the name of the popular cactus, Cephalocereus senilis (sef-ah-loh-see-ree-us sen-ill-us). If we told you that cephalo refers to the head, cereus suggests to tall, candle-like appearance and senilis means old or white-haired, you could visualize what this cactus should look like. Cephalocereus senilis, more commonly called old man cactus, is indeed a tall, candle-shaped cactus covered with a mass of white wooly hair.

When you come across a cactus with a name like Trichocereus peruvianus, you would be correct in assuming that its native habitat is Peru and that Euphorbia horrida is, in fact, somewhat ferocious. Likewise, Echinocactus horizonthalonius, better known as the Mexican mule clipper because of its spreading, horizontal growth habitat, is used as a barrier to animals from straying too far.

But what about names like Agave victoriae-reginae and Selenicereus macdonaldiae? Perhaps Selenicereus sounds like Latin-but macdonaldiae? We mentioned that plants can be named for people. It’s quite common, in fact, for a new species to have the same name as its discoverer. For example, if Olivia Johnson discovered a rare species of Opuntia near Omaha and wanted to name it after herself, she might call it Opuntia oliviae (in Late, -ae is the feminine ending). On the other hand, if she wanted to include her husbandin on the festivities, she could call her discovery Oputnia johnsonii (-ii ending is the masculine form).

However, if by some chance another cactus collector found a rare species of Opuntia and referenced it with the identical name-only one week earlier-Olivia would have to try again. The rules say that no two plants can be given the same botanical name. But Olivia need not give up so easily; she could always call it Opuntia onahensis. After all, she did find it near Ohmaha.

The terms such as family, genus, species, and variety will be clearer if you understand how the names relate:

  • One variety makes up a species
  • One species or more make up a genus
  • One genus or more makes up a family

In a name like Opuntia microdasys rufida, Opuntia is the genus, micordasys is the species and rufida is the variety. The family, of course, is the cactus family.

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Tribes & Subtribes

Tribes and Subtribes are used by modern taxonomists. They basically classify the cactus family by dividing the genera into a group of tribes and subtribes.

The following tribes exist in the Cactaceae Family:

  • Pereskieae
  • Opunitieae
  • Cacteae

These three tribes group together all of the different genera in the Cactus family. Tribes make it much easier to classify and discuss cacti without having to include the extensive genera. I will take each tribe and break it down into subtribes and identify most of the genera and species that exist in each of the three tribes.

1. The first tribe I will distinguish will be the Pereskieae tribe. This tribe only contains two genera: Pereskia and Maihuenia. There are no subtribes in the Pereskieae Tribe.
“All of the genera in this group are plants with woody stems, erect or sarmentose; leaves persistent or semideciduous. Areoles are spiny and more or less woolly at the leaf axils. Flowers pendulous, solitary or in clusters; fruit fleshy.”
Simon and Shuster’s Guide to Cacti and Succulents

2. The Opuntieae tribe principally consists of the genus Opuntia with its subgenera Consolea, Opunita, Cylindropunita, Tephrocactus. Don’t get subgenera confused with subtribes.

“The Opuntieae are usually very fleshy, branched plants, with consecutive branches that may be either rounded or flattened, studded with areoles, with or without spines but always bearing glochids. Leaves flat or cylindrical and generally caducous apart from a few exceptions with more or less persistent leaves. Spines are usually straight and slender, sometimes hooked or with a protective sheath. Flowers, borne singly on the areoles, are sessile; the corolla is formed from numerous sepals and colored petals. The fruit is a berry with numerous seeds and is often edible.”
Simon & Shuster’s Guide to Cacti and Succulents

3. The Cacteae is the largest tribe in the Cactaceae (Cactus) Family. In fact it comprises of three-quarters of the family’s species, therefore it is broken down into subtribes.

The Cacteae Tribe

SubtribePrinciple Genera
CerinaeCereus, Cephalocereus, Oreocereus, Pachycereus, Heliocereus, Trichocereus, Cliestocactus and Espostoa
HylocereinaeHylocereus, Selenicereus and Aporocactus
EchinocereinaeEchinocereus, Echinopsis, Lobivia
EchinocactinaeEchinocactus, Ferocactus, Gymnocalycium, Neoporteria, Parodia, Stenocactus, Echinofossulocactus
CactanaeMelocactus, Discocactus
CactinaeMammillaria, Coryphantha, Thelocactus, Escobaria
EpiphyllinaeEpiphyllum, Phyllocactus, Zygocactus, Schlumbergera
RhipsalidinaePhipsalis, Hatiora, Lepismium