This succulent plant comes from Mexico and forms stemless rosettes of thick silvery-grey leaves that have very sharp spines. They can grow to 1.8m in height and eventually form big clumps by suckering. I remove these, as I want the effect of a single plant. The plant needs full sun and good drainage - it is quite drought tolerant. It can be grown in a large pot. Propagation is by offsets. There are variegated cultivars, including 'Marginata'. It provides strong architectural form in the garden. It is apparently monocarpic, with rosettes dying after flowering, but mine has shown no sign of flowering yet and I have had it for about five years.
Postscript: My two silver-grey specimens of this plant that I had for a number of years near my front door grew to be enormous. They had such sharp, dangerious points on their leaves and they started suckering madly, and these became difficult to remove because of the spikiness of the leaves. In the end I took the plants completely out. In a large garden, they could have a place.