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Peyotl zacatecasensis
The peyote is an allucinogen, non-spike cacti listed as a threatened specie according to Mexican environmental laws. In this particular case, this bunch was found on a cinegetic ranch nearby Reynosa, Tamaulipas. Aproximately 1,500 individual were counted only on a 10 x 10 m square, so imagine the total number of them along a 5 km transect....
It was found on a relict of Tamaulipan thornscrub near Reynosa, with several mezquite trees (Prosopis glandulosa)
Very cool that you saw this in the wild. I've provided the correct scientific name and a reference link for some more info.