24 May, 2010

What is the difference between a Cactus and a Succulent?

Well, to completely confuse you in the first sentence –
Cacti are actually succulents!!!

“How is that?” you ask? Let me explain…

Succulents are a group of plants that are identified as having cells in parts of their body that retain water:
  • Some plants have these cells in their roots, like some Euphorbias.
  • Others have them in their stems, like Stapliads and Pachypodiums.
Cacti also have this ability and this is why a cactus is a succulent. It is similar to the saying, “All German shepherds are dogs, but not all dogs are German Shepherds.” All Cacti are succulents, but not all succulents are cacti.

So what defines a cactus?
All cacti belong to the plant family Cactaceae, and there are many characteristics that identify a plant as belonging to this family. SPINES are not one of them!

Don’t get fooled into thinking that a cactus is a cactus just because is has spines. There are many species of succulents with spines that aren't in the Cactaceae family, such as some Euphorbias and Agaves. On top of that, some cacti don’t have spines at all, like most Lophophoras.

What defines true cacti are areoles. Areoles are what spines, glochids, branches and flowers may sprout from, and all cacti have them, while succulents do not. Areoles are not hard to find – they usually look like small, fluffy, cotton like lumps on the body of the cactus:

Photo 1:
The cactus Trichocereus sp. with white, cotton like areoles.
Photo 2: Another cactus, Trichocereus sp. also with white, fluffy areoles.
Photo 3: The succulent Euphorbia trigona, which has spines but no areoles.

So, the next time you look at a succulent, look to see if they have areoles. Then you will know for certain that it is a cactus, or not. Remember though, there are exceptions to every rule, and cacti are the hardest of all plants to identify. Be prepared for a lot of research and patience if you wish to identify what species of cactus your plant is.

For more information, visit www.fickleprickles.com.au

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