Mexico can roughly be divided into two geological zones: The eastern zone with the Sierra Madre Oriental, which mainly consists of calcareous sedimentation and the western and southern zones with the Sierras Madre Occidental and del Sur which are of volcanic material. Coryphantha spp. grow in both zones,but the species are specialised either for lava soils or for calcareous soils.An exception is C. clavata which is known to grow on volcanic stone in one location, while otherwise this species grows on calcareous ground.
Coryphantha spp. are not extreme endemites, which occur on strictly defined soil or ground only. Usually, a few main parameters like lava/lime, exposition, incline etc. are sufficient for the occurrence of a species. Most probably, the limits of distribution of the species are caused by climatic factors. This would also explain the rather huge distribution area of certain species like C. ele-phantidens (in this case from southern Oax-aca and Veracruz up to Zacatecas), which can be found wherever their specific demands for a location are fulfilled.
A few species are specialised for special soils:
C. gracilis grows on very characteristic conglomerate soils only, or C. jalpanensis, which grows on raw humus on calcareous rocks only. For other species with very limited areas, like C. pulleineana or C. vogtherriana, the reason for their limited distribution is not known, but it is certainly not caused by geological conditions.
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