Dichotomous branching, i.e., forking or dividing into two parts, is one of the characteristics of the M. karwinskiana ssp nejapensis. Although it is not a common occurrence in cacti in general, it happens for some reason in this particular subspecies. What is interesting about this cactus is that it began as a single head, and it has now divided twice, forming what will be four separate branches. When the division process started, it was obvious that four heads would appear, but I don’t think the one head divided quadruply. Most probably, one head became two, and then those two immediately divided.
This subspecies is native to the area around the city of Nejapa in the state of Oaxaca in Mexico, hence the subspecies name. It has small white flowers with a red middle-stripe, which appear in early summer. It requires light shade in summer in Phoenix, and regular watering. Another characteristic of this subspecies is the abundance of wool at the areole. This cactus also branches from the base.
There is one other Mammillaria, M. parkinsonii, commonly called Owl Eye Cactus, known for dichotomous branching. I wrote about it in an earlier post. Look at the photo and you will understand why it’s called Owl Eye!