A tropical cactus that was once found in the Florida Keys no longer exists in the United States, save for some conservation collections, a field biologist told Fox News Digital this week.The Key Largo tree cactus was wiped out by rising sea levels in the region, among other factors, according to Jennifer Possley, who wrote about its demise in a paper published earlier this month in the Journal of the Botanical Research Institute of Texas.Possley is director of regional conservation at Fairchild Tropical Botanical Garden in Coral Gables, Florida, near Miami. She's part of a group of scientists and researchers