The genus Mammillaria is one of the largest groups in the Cactus Family (Cactaceae), with the majority native to Mexico. Often, their flowers come in a ring around the top of the stem, as can be seen here. Mammillaria hahniana is quite variable in its spines and wool, with some widely-grown forms having a much shaggier appearance than the plant pictured. It is native to east-central Mexico.
More saffron! Six flowers harvested so far, at least three more are coming. I’m so glad these bloomed this year, I had just about given up waiting on them.
Kihaku-Gato's Garden Blog (tumblr import) 