Cactus
A specific family of plants (Cactaceae) native to the new world containing approximately 2,500 species (about 1/4 of all succulent plants). All Cactus are succulent and are identified by their leaves that have been modified into 'spines'.

Caudex
A storage organ on some root succulents that grows at ground level or below. This is really part of the stem of the plant and often times growers raise this out of the ground even more than in nature to show off the attractive stem/root as a feature of the plant. It generally increases in size as the plant grows/get older.

Convergent Evolution
When two or more otherwise unrelated plants from different geologic locations evolve similar characteristics to adapt to a similar set of conditions present. There are a number of such examples among the succulent plants of the world such as some of the columnar cactus of the Americas and some of the Euphorbias of Africa and Madagascar. See What is a Succulent? for more information and pictures of examples.

Crest
A mutation that affects the growing tip of the plant that forms a long line rather than a single point. It is unknown exactly why this occurs but has been noted in almost every type of plant. Often this mutation inhibits flowering and therefore natural reproduction of the plant.

Cristate
See Crest

Succulent
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). Succulent plants have adapted several different ways to store and conserve water for times of need.; There are stem succulents that store water in the stem of the plant... like most of the familiar local cacti. There are root succulents such as: where water is stored in the roots or a caudex, examples are: peniocereus greggii (queen of the night), and the adeniums and pachypodiums (Madagascar palm). Finally there are leaf succulents such as the agaves and aloes that store water in a succulent leaf.