All variegates are mutants. Something has gone wrong with the cellular structure of the leaf or stem growth tip (apical meristem) of the plant.
Sometimes called "Living Stones".
These 2 caudiciform genera, are unrelated except that they are both from Africa and Southeast Asia and are named after the country Aden.
These 3 genera, in the Crassulaceae family, include plants from many parts of the world.
The Bromeliads, like Cacti and Agavaceae are a New World family.
There are around 200 species in the genus, most from Mexico, some from the southern United States and into South America.
Both genera are from South Africa and are closely related.
Aloe, is a genus containing about four hundred species of flowering succulent plants. The most common and well known of these is Aloe vera, or "true aloe".