The greatest diversity in Mammillaria
occurs in Mexico, in rocky sites bordering, but not in, semidesert. Some latex-bearing species, such as M. lasiacantha
and many Mexican taxa, have their latex ducts deep inside the cortex, not in the tubercles. When preserving specimens outside the flora area, location, color, and viscosity of latex should be carefully recorded after plants have been cut and the latex allowed to ooze from its ducts for a few minutes. The latex ranges from sticky and white to less viscous and translucent. Tubercle length in descriptions refers to the distance the tubercle protrudes or projects outward from the stem axis. Fruits with mature, viable seeds sometimes remain on the plants for months before or after ripening. The time given in each phenology statement refers to the time of first ripening of the fruit (not seeds). Seeds or dried remains of fruits often may be found deep in the axils of the tubercles, hidden by spine clusters or even pulled below the level of the soil.