Description:Mammillaria standleyi is a very variable species with white wool between the tubercles, particularly towards the apex, with white radial spines and brownish centrals. It form a complex of related species along with Mammillaria canelensis, Mammillaria hertrichiana, Mammillaria miegiana, Mammillaria montana, Mammillaria movensis, Mammillaria sonorensis, Mammillaria tesopacensis, & several more. It is still unclear whether this variable complex is one or several species. There is so much variation in characters such as spination, woolliness, and flower colour that most authors choose to lump them together until further studies are done.
Habit: Plants usually solitary but at times forming large clumps of nearly 1 meter wide, densely covered with spines;
Central spines: (2-)4, reddish brown, longer and stouter than the radials, erect, 5-9 mm long.
Radial spines: About 16, slightly spreading, white with darker tips, 4-8 mm long.
