Mammillaria karwinskiana subs. nejapensis (Mammillaria nejapensis) is very variable, especially for the length of the spines. This particular specimen has a marble-like variegation on its tubercles. It is commonly called "Owl Eye Cactus", known for dichotomous branching (forking or dividing into two parts). Although dichotomous branching is not a common occurrence in cacti in general, it happens for some reason in this particular species. What is interesting about this cactus is that it began as a single head, one head became two, and so on.