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Climate change and sea level rise have contributed to the extinction of the Key Largo tree cactus

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It is now believed to be the first local extinction of a species caused by sea level rise in the United States, according to researchers at the Fairchild Tropical Botanic Garden.

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The last known stronghold of the giant Key Largo tree cactus in the country was a limestone island in a remote mangrove forest, where the cactus bloomed in anonymity and garlic-scented flowers indefinitely.

But under the onslaught of brackish water in a warming world, the cactus, discovered in 1992, withered.

It is now believed to be the first local extinction of a species caused by sea level rise in the United States, according to researchers at the Fairchild Tropical Botanic Garden in Coral Gables and multiple state and local government agencies.

A study published Tuesday in the Journal of the Botanical Research Institute of Texas details the demise of the only Key Largo tree cactus, first found three decades ago and featuring 150 sturdy stems that could grow up to 20 feet (6 meters) tall.

By 2021, only six diseased fragments of the cactus remained. When it became clear that they would not survive, scientists collected them in the hope of keeping the legacy alive in a nursery.

“I liken it to losing a historic work of art,” said Jennifer Possley, director of regional conservation at Fairchild Tropical Botanic Garden and lead author of Tuesday’s report. “It’s part of our story, and in this case, it’s a charismatic part of our natural history. It’s a cool plant, and now it’s gone.”

The Key Largo tree cactus still grows in the Caribbean, including parts of the Bahamas. The creamy white flowers reflect the moonlight and attract pollinators such as bats and sphynx moths. The cactus bears purple fruits with lots of seeds for birds or furry locals.

In its lonely Key Largo post, the cactus has also been a victim of hurricanes, including Hurricane Irma in 2017, which flooded parts of the island with damaging saltwater for weeks. Unknown critters preyed on the cactus, possibly attracted by the high water content when freshwater was scarce, scientists said.

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Possley, however, says the cactus could have survived the occasional hurricane and its pests if sea levels hadn’t risen, which has caused increasing flooding in the fall months and stripped soil from the cactus’ limestone base.

“Most of the other rare plants we work with don’t just grow in one place,” Possley said. “Sea level rise was the nail in the coffin for this one.”

According to the Florida Climate Center, sea level rise in the southeastern United States has been about 0.12 inches per year since the early 1990s, but this varies by area.

At Virginia Key, an island off the coast of Miami about 50 miles north of Key Largo, sea levels have risen 8 inches since 1950. And the trend is accelerating. Sea levels have risen 1 inch every 3 years over the past 10 years, according to tide gauge data.

A 2022 report from the National Oceanic and Atmospheric Administration found that sea levels along the U.S. coastline will rise an average of 10 to 12 inches (25 to 30 centimeters) by 2050, the same amount as the rise measured in the 100 years leading up to 2020.

“We are on the front lines of biodiversity loss,” said George Gann, co-author of the Key Largo cactus study, in a prepared statement. Gann is executive director of the Delray Beach-based Institute for Regional Conservation.

“Our research in South Florida over the past 25 years shows that more than one in four native plant species is critically endangered or already extinct in the region due to habitat loss, overcollecting, invasive species and other causes of degradation,” Gann said.

Other co-authors of Tuesday’s report include researchers from the Florida Department of Environmental Protection and the U.S. Department of Agriculture.

Extirpation is the loss of something in a localized area. Extinction means the loss of something on a more global scale.

The Center for Biological Diversity concluded in a 2013 study that 233 endangered species in 23 coastal states are at risk from sea level rise, including the endangered Key deer.

“This means that, if left unchecked, rising sea levels threaten the survival of 17 percent (one in six) of our nation’s federally protected species,” the report said.

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When the species was first discovered, some scientists thought the Key Largo tree cactus stand was a unique population of the similarly named Key tree cactus. The Key tree cactus was listed as federally endangered in 1984, and between 1994 and 2007, the population declined by 84%.

The two plants look similar with tall stems and similar flowers. However, the Key Largo variety has long tufts of woolly hair at the base of the flowers and fruits. The spines of the Key Largo cactus are also twice as long as those of the Key tree variety.

In 2019, the Key Largo tree cactus was confirmed to be the first and only known flora of its kind in the United States, according to a study by Alan Franck, herbarium collection manager at the Florida Museum of Natural History.

Possley said there are preliminary plans to plant some of the nursery-grown Key Largo tree cactus in the wild. She said they have thousands of seeds, several tall plants and have found an area where they could potentially grow outside of the nursery.

“But there is no place that is perfect anymore,” Possley said.

Kimberly Miller is a reporter for The Palm Beach Post, part of the USA Today Network of Florida. She covers real estate and how growth is impacting the South Florida environment. Subscribe to The Dirt for a weekly real estate digest. If you have news tips, send them to [email protected]. Support our local journalism: subscribe today.