Surprisingly, Mammillaria pectinifera is closely related to M. carmenae (which looks completely different & is also profiled on Sentient Meat), M. glassii, M. picta, M. plumosa, and M. prolifera. Together these species plants form a clade, a group of types likely descending from a common ancestor. They differ markedly from each other in size, spines, and other features.
My plant is just over an inch in diameter. This is its first bloom under my care. The flowers are an elegant pale pink. Overall the plant is neat and understated in appearance.
Mammillaria pectinifera's appeal may be its downfall. It is reported to be nearly extinct due to over-collection within its native Puebla, Oaxaca, Mexico. Consequently, it's protected under CITES I, the most stringent protocol of international protection.