What is the size of a cactus?

The size of a cactus depends upon the type. For example, some cactus plants are naturally taller, such as the 40 foot/12 meter giant saguaro cactus [Carnegiea gigantea] and the 50 foot/15 meter old man cactus [Cephalocereus senilis]. And some cactus plants are naturally smaller, such as the 2 inch/5 centimeter living rock or fossil cactus [Ariocarpus fissuratus] and sea urchin or silver dollar cactus [Astrophytum asterias].

The size also depends upon environmental conditions. For example, cactus plants may not do as well outside their native habitat despite vigilant care. The normally towering old man cactus in the wild tends to grow no taller than 3 feet/90 centimeters in cultivation.