As with several dozen other cactus species, mammillaria pottsii
grows in the US only in the Big Bend region of far west Texas, and is uncommon in the wild. Stems are small; up to 6 or more inches tall but only around an inch in diameter, cylindrical or club shaped (wider towards the apex). Plants readily form large clusters, branching both from the base and along the stems. Areoles usually have between 43 and 60 spines, colored white, grey, light brown or pale red. Radial spines are very short and thin, but the 6 to 12 central spines are thick and rigid, pointing outwards at a range of angles, and around half an inch in length. Flowers and fruits are red.