Stem succulents are fleshy
succulent columnar shaped plants which conduct photosynthesis mainly through stems not leaves. They are related by form, but not by evolution. They evolved to have similar forms and physiological characteristics by
convergent evolution. Examples are tall thin
Euphorbias from deserts and arid regions southern African and Madagascar, similarly shaped cacti from North America and South America, which occupy a similar evolutionary niche, and members of two genera of the family
Asclepiadaceae (
Hoodia and
Stapelia). Shared features are a succulent stem that stores water and conducts photosynthesis, protective
spines or
thorns, no leaves (or highly reduced leaves), and use of
CAM photosynthetisis (an opening of
stomata and fixing CO2 almost exclusively at night).