Euphorbia Fat Plant Primer
In the vast world of succulent Euphorbia species, there are many, mostly from southeast Africa and Madagascar that are prized for their ability to form thick trunks and/or tuberous roots. Many are rarely seen in the trade. However, some find be found offered by independent garden centers and seasonal cactus and succulent sales where the vendors are usually hobbiests themselves. Of the many caudex forming euphorbia we have had exposure to we can group the most popular ones into three or four identifying categories based on their characteristics.
You have plants that form a caudex under a thick canopy of horizontal branches with non-succulent leaves such as Euphorbia decaryi. Then there are many euphorbia with thick succulent stems with spines mounted on a trunk with tuberous roots such as Euphorbia knuthii. Some of the rarer caudex forming euphorbia have a large melon shaped base and a small canopy of non-succuelnt leaves such as Euphorbia maritae. Then finally, many of the Medusa Head Euphorbia form a thick trunk under a pin-wheel shaped head. Here are a few examples of these four basic types of caudex forming Euphorbia.
A short List of Caudex Forming Euphorbia Plants
Type 1 - Many horizontal branches with thick trunk and/or tuberous roots
This type of Euphorbia has many branches that tend to lay down to form a thick canopy that hides the caudex base. The branches are typically dark colored, about 1 centimeter thick, and have small flat leaves. You can trim some of the branches to expose the thick trunk.
Type 2 - Thick Succulent Spiny Stems on Tuberous Roots
This type has thick succulent spiny branches mounted on thick tuberous roots. The stems can be upright or drooping.
Type 3 - Euphorbia with large bases and non-succulent leaves.
Type 4 - Euphorbia Medusa Heads with Fat Trunk.
Some Medusa Head Euphrobia, such as E. esculenta, can produce very fat trunks as 6-7 (18-21 cm) inches wide. Medusa Head euphorbia are typically characterized by a stem that is pinwheel shaped when looking at the top.
These are just a few of the many caudex forming Euphorbia. There are many more, even within each type. It's a lifetime of learning.