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What is a Succulent? What is a Cactus?

by Kevin Barber

What a great question. . . glad you asked it!

A succulent is a plant that stores water for times when water is not available to it. Succulent plants are generally found in arid environments such as deserts and semi-deserts. However, they can also be found in areas where the annual rainfall is high but not reliable (for instance most of the annual rainfall comes once or twice a year in quick bursts).

What are the different types of Succulents?

There are three basic types of succulent plants, identified by where they store their water. In their roots, in their leaves and in their stems.

Stem Succulent; Organ Pipe Cactus
Stem Succulent:
Organ Pipe Cactus

Leaf Succulent: Aloe
Leaf Succulent:
Aloe
Root/Caudex Succulent: Adenium
Root/Caudex Succulent:
Adenium

Why do so many of the succulent plants from different parts of the world look similar?

Convergent evolution has provided an interesting array of different families of plants that have adapted to similar arid environments in different parts of the world. Plants have adapted from different ancestors to meet the challenges of a similar arid environment. For instance the Senita of Mexico is similar in appearance and adaptation to it's environment as the Euphorbia pictured here from Madagascar. They both fill a similar niche in the ecosystem of their respective habitats.

Euphorbia from Madagascar
Euphorbia sp from Madagascar
Senita Cactus from Mexico
Senita Cactus from Mexico

What is the difference between cactus and succulents? Are all succulents cactus?

There are many thousands of plants that can be categorized as succulents in dozens of different botanic families. One of the more well known families of succulent plants here in Arizona that is unique to the new world are the Cacti. So all cacti are succulents but not all succulents are cacti.

What are some of the families or groups of succulents?

There are six major families of plants whose members are all succulent or at least mostly succulent. They are: Asclepieadaeae, Asphodeliceae, Cactaceae, Crassulaceae, Euphorbiaceae and Mesembryanthemaceae.

There are also a number of other families that have at least a few members that are succulent in nature; they include: Bromeliaceae, Passifloraceae, Apocynaceae, Didiereaceae, Portulacaceae, Sterculiaceae, and Burseraceae.

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