Carnegiea is the genus of a single species, C.gigantea, otherwise known as the giant cactus.
These plants can grow over 40 feet tall. Their areoles (small light- to dark-coloured bumps from which grow clusters of spines) bear brown wool with many spines. Flower will appear near the top of plant when it is mature.
A suitable soil should contain potting compost with extra sharp sand or brick rubbles. The pot should be large enough to stop the plant from falling over. They should be repotted every four years unless the plant becomes too large for the pot and watered from March to September when the soil dries out.