First U.S. vascular plant extirpation linked to sea level rise? Pilosocereus millspaughii (Cactaceae) in the Florida Keys, U.S.A.

The global biodiversity crisis affects species across all continents and taxonomic groups. Direct destruction of species and habitats has been a primary driver of declines, though climate change and associated sea level rise are expected to accelerate loss. The flora of low-lying, relatively isolated islands is especially threatened when high species richness intersects with vulnerability to sea level rise. The Florida Keys represent a hotspot for cactus diversity in the eastern United States, with eight species recognized, three of which are endemic to the islands. Though not endemic to the islands, the Key Largo tree cactus (Pilosocereus millspaughii) was known in the United States from only a single population in the Florida Keys. Its decline and imminent extirpation correspond with rising sea levels in the region. The other cacti in the region, and all rare plants in the Florida Keys, are threatened with a similar fate.