Ariocarpus retusus, from northern and central Mexico is the largest and fastest growing Ariocarpus. It can reach flowering size (10 inches) in six to eight years, whereas the other species can be as much as twenty years old. Unlike A. fissuratus it's tubercules are smooth and the plant produces considerable amounts of wool between them. A mature specimen can look remarkably like a giant wooly artichoke. I bought this one from Miles 2 Go in Tucson and he showed me some of his specimen plants. One was nearly the size of a bowling ball and nearly completely covered in wool. It was very cool!
     Like other Ariocarpus it has a large tap root and shrivels down to the ground in times of drought. It produces showy white to pink flowers in fall.