Imagine a botanical garden, and acres of carefully designed, highly manicured, delicately pruned “zoos for plants” may come to mind. But at El Charco del Ingenio, a botanical garden and natural protected area in central Mexico, the sprawling scrubland has been allowed to return to its unencumbered, wilder roots. The approximately 160-acre property, acquired from several different families, had been overgrazed for hundreds of years, according to M…