4.1.3. Calcium Carbonate

The pith of *Ariocarpus retusus* subsp. *trigonus* presented weak peaks belonging to calcium carbonate as reported by Palacio et al. [39] for some gypsophilic plants.Monje and Baran [40]identified on stems of another cactus, *Cylindropuntia kleiniae* (DC.) F.M. Knuth, vibration in the infrared between 1415 and 1422 cm−1; they were assigned to the carbonate antisymmetric stretching mode of calcite. Anatomical techniques allow the identification of biominerals in certain plant tissues, however, during fixation with substances such as acetic acid, some calcium salts and phosphates could be lost [41–43]. This may be the case detected here in the pith of *Ariocarpus retusus* subsp. *trigonus*, since no previous report of calcium carbonate for any member of Cacteae is known. Probably calcium carbonate is rare in the group because they were not detected in the other species studied, even when the same method to separate biominerals were applied.
