Biscayne National Park is home to hundreds of species of plants, including several endangered species. The most interesting of the park's plants are perhaps the mangroves, which are tolerant of a wide range of salinities. In 2001, it was discovered that the park shelters the rare semaphore prickly-pear cactus, which grows only in South Florida. Botanists have found 570 of the plants on an island in Southern Biscayne Bay. The cactus is a candidate for the federal endangered species list.
The endangered Sargent's Palm also exists in Biscayne National Park. It is considered to be the rarest palm native to Florida. It was initially found on Elliott Key and Sands Key, but collectors in the late 1800's began to harvest them for ornamental use. In 1991 only 50 palms were found on Elliott Key. Many were also damaged in Hurricane Andrew. Today there are about 16 plants on Elliott and 123 on Long Key thanks to efforts undertaken to reintroduce palms on three of the original islands.