“It’s a big deal when we lose species from an entire country,” said George Gann, executive director of the Florida-based nonprofit Institute for Regional Conservation.

Scientists have warned for a while that global warming threatens to batter many species. The loss of this cactus underscores how climate change is driving extinctions in real time — not in the future, but today.

“For me, it was devastating,” said Jimmy Lange, a research botanist at the Fairchild Tropical Botanic Garden in Florida who monitored the Key Largo tree cactus for years. Lange, Gann and other researchers described the local extinction in a study published Tuesday in the Journal of the Botanical Research Institute of Texas.

“This is such a glorious plant,” Lange said.

The tree cactus persists elsewhere in the Caribbean, including parts of Cuba and the Bahamas. But the stand lost on Key Largo to saltwater intrusion from rising seas and soil depletion from high tides and hurricanes was the only one known in the United States. This coastal plant with the snowy fur is Florida’s latest victim of sea-level rise, fueled by the melting of glacial ice thousands of miles away.

Discovered in 1992, this solitary stand of Key Largo tree cactuses sprouted from a limestone outcrop bordered by mangroves on Key Largo, a 33-mile-long island south of Miami popular with tourists. At night, its cream-colored flowers reflected moonlight and attracted bats that acted as pollinators. The magenta fruit that grew from the pollinated plants lured hungry birds and mammals during the day.

Botanists first noticed a problem in 2015 when they discovered something had almost entirely chewed through many of the cactus stems, probably in search of water. Only 60 individuals were left alive; half the population was gone.

The perpetrator may have been a raccoon or rat, though a wildlife camera never caught a culprit. “We’re not 100 percent sure,” Lange said. The team began rescuing stem fragments the following year.

Then in 2017, Hurricane Irma sent a 5-foot storm surge through Key Largo. The cactuses had endured hurricanes before, but the rush of seawater from that Category 5 storm accelerated the die-off. Past research has shown higher mortality rates for tree cactuses in saltier soil.

Even after the skies cleared, “king tides” boosted by sea-level rise continued to bring destructive saltwater within inches of the plants. The higher tides may have even made freshwater less available to small mammals and prompted the frenzy on the cactuses stems to quench their thirst. “But we can’t say for sure,” Lange said.

“The population was just slowly, and then quickly, collapsing,” Lange added.

With little hope of recovery, the team dug up the last six individuals to bring into human care. Today, about 60 Key Largo tree cactuses are cultivated at two nurseries in Florida while more than 1,000 seeds are kept in storage at Fairchild and at an Agriculture Department seed bank in Colorado.

The research team said it believes the cactus is the nation’s first vascular plant to go locally extinct due to sea-level rise. Vascular plants are a large group that include ferns, conifers and flowering plants.

Despite their hardy appearance and ability to thrive in arid environments, cactuses are among the most endangered organisms on Earth. Increasing temperatures are testing their heat tolerance. Rising seas threaten to inundate coastal cactus species, including others in the Florida Keys. Far from the ocean, fiercer wildfires fueled by invasive grasses are putting the giant saguaro, that icon of the American West, at greater risk.

While the illegal collecting of cactuses has historically been a big threat, climate change is expected to become the primary driver of cactus extinction in the future.

For the Key Largo tree cactus, there’s still hope. The botanists who rescued the plants want to reintroduce it back to the wild someday — at a higher elevation.

“There is some degree of optimism,” said Alan Franck, collections manager for the herbarium at the Florida Museum of Natural History. “There are many species we’ve lost from Florida and the country that are not in cultivation.”