In this Nov. 4, 2015 photo, Dr. Salvador Arias is seen past a cluster of endangered echinocactus grusonii cacti, also known as Biznaga, as he looks at other species inside the botanical gardens of the National Autonomous University of Mexico in Mexico City. About a third of the world’s cactus species are threatened with extinction, the International Union for Conservation of Nature warns in a new report. (AP Photo/Rebecca Blackwell)