The Key Largo Tree Cactus Extinction: How Rising Seas Claimed This Florida Gem

The Key Largo tree cactus (Pilosocereus millspaughii), once a towering symbol of resilience in Florida’s subtropical landscape, has vanished from the United States. In a heartbreaking milestone, it became the first U.S. species driven to local extinction by rising sea levels. 

Discovered in 1992, this charismatic cactus thrived in a single patch in the Florida Keys, surrounded by mangroves on a low limestone outcrop. By 2021, only six sickly stems remained. Today, none grow naturally in the U.S. 

This isn’t just a story about a cactus—it’s a warning of what climate change could mean for coastal ecosystems worldwide. In this guide, we’ll explore the rise and fall of the Key Largo tree cactus, its ecological significance, the forces that led to its demise, and what its loss signals for the future.

What Was the Key Largo Tree Cactus?

The Key Largo tree cactus was no ordinary plant. Standing up to 20 feet tall, it was a giant among cacti, with ribbed, blue-green stems that branched out like a candelabra. Its creamy white flowers, blooming under moonlight, gave off a faint garlic scent, attracting bats and sphinx moths as pollinators. 

The cactus’s vivid reddish-purple fruits drew birds and mammals, making it a vital part of its ecosystem.

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What set it apart from its close relative, the Key tree cactus (Pilosocereus robinii), were its long, woolly hairs at the base of its flowers and fruits—thick enough to look like drifts of snow in the Florida heat. Its spines, twice as long as those of its cousin, added to its striking appearance.

First identified in 1992 in a two-acre patch at John Pennekamp Coral Reef State Park, the Key Largo tree cactus was the only known U.S. population of Pilosocereus millspaughii. While it still grows in parts of the Caribbean, including northern Cuba and the Bahamas, its U.S. presence was unique. 

The cactus thrived on a limestone outcrop, surrounded by mangroves, in a delicate balance of soil and organic matter. For decades, it stood as a testament to nature’s ability to adapt to harsh conditions.

But that balance was fragile, and the forces of climate change were about to tip the scales.

The Forces Behind Key Largo Tree Cactus Extinction

The extinction of the Key Largo tree cactus wasn’t caused by a single event. It was a slow, relentless assault by multiple environmental pressures, all tied to human-driven climate change. Let’s break down the key culprits.

Rising Sea Levels and Saltwater Intrusion

The Florida Keys sit just a few feet above sea level, making them one of the most vulnerable regions in the U.S. to rising seas. Since the early 20th century, global sea levels have risen about 8–9 inches, with the rate accelerating in recent decades. 

In South Florida, sea level rise is driven by melting ice sheets in Greenland and Antarctica, as well as thermal expansion of warming ocean waters. For the Key Largo tree cactus, this meant trouble.

The cactus grew on a low limestone outcrop, surrounded by mangroves that acted as a buffer against the sea. But as sea levels rose, saltwater began creeping into the mangroves. This saltwater intrusion increased soil salinity, disrupting the delicate ecosystem that supported the cactus. 

Unlike mangroves, which can tolerate some salt, the Key Largo tree cactus was not adapted to such conditions. The salt stressed the plants through osmosis, pulling water from their cells and causing ionic imbalances.

Over time, the soil and organic matter that anchored the cactus eroded away, leaving it exposed and vulnerable.

By 2011, researchers noticed saltwater flooding from king tides—exceptionally high tides that occur during new or full moons—reaching the cactus’s habitat. These tides, worsened by rising seas, brought destructive saltwater within inches of the plants. 

In 2019, king tides flooded parts of Key Largo for three months straight, a phenomenon unheard of in previous decades. The cactus, already struggling, had no chance to recover.

Hurricanes and Storm Surges

The Florida Keys are no strangers to hurricanes, but the intensity and frequency of these storms have increased with climate change. The Key Largo tree cactus weathered storms like Hurricane Georges in 1998 and a series of hurricanes in 2005 without significant losses. 

But Hurricane Irma in 2017 was a game-changer. A Category 5 storm, Irma unleashed a 5-foot storm surge that inundated Key Largo for days. The surge flooded the cactus’s habitat with saltwater, further eroding the soil and organic matter it depended on.

The aftermath was devastating. The mangrove ecosystem, already weakened by rising seas, was in tatters. The cactus population, which had numbered about 150 stems in 2011, plummeted. By 2016, only 28 rooted stems remained. 

The storm surge didn’t just drown the plants—it accelerated soil depletion, leaving the cacti with little to anchor them. Researchers noted that salt-tolerant plants, previously confined to brackish soils beneath the mangroves, began creeping up the outcrop, a clear sign that salinity was increasing.

King Tides and Prolonged Flooding

King tides, which occur seasonally in the fall, became a recurring nightmare for the Key Largo tree cactus. These tides, amplified by sea level rise, brought prolonged flooding to the low-lying outcrop. 

In 2019, the flooding lasted for over three months, submerging the cactus’s habitat in saltwater. This wasn’t a one-off event—king tides were becoming more frequent and severe, a direct consequence of rising oceans. 

The prolonged exposure to saltwater further stressed the cacti, weakening their ability to photosynthesize and reproduce.

Herbivory: A Surprising Culprit

As if rising seas and storms weren’t enough, the Key Largo tree cactus faced an unexpected threat: herbivory. In 2015, researchers observed significant damage to the cacti, with large portions eaten by mammals. They suspect that small animals, possibly raccoons or Key Largo woodrats, were driven to the cacti by a shortage of freshwater. 

As saltwater intrusion reduced available freshwater in the mangroves, these animals turned to the cactus’s water-rich stems for hydration. This herbivory event was unprecedented in the Lower Keys, where flooding had historically been less severe.The damage was catastrophic. 

By 2015, the cactus population had dropped from 150 to 60 individuals—a 50% decline in just two years. Efforts to identify the culprits with cameras were unsuccessful, but the impact was undeniable. The combination of herbivory and environmental stressors left the cacti in a death spiral.

The Decline: A Timeline of Loss

The Key Largo tree cactus’s decline was a slow-motion tragedy, documented by researchers from the Fairchild Tropical Botanic Garden, the Florida Museum of Natural History, and the Florida Department of Environmental Protection. Here’s a timeline of its downfall:

• 1992: The Key Largo tree cactus is discovered in a single population of about 150 stems in John Pennekamp Coral Reef State Park. Initially thought to be a unique population of the Key tree cactus (Pilosocereus robinii), it’s later identified as Pilosocereus millspaughii.
• 2007: Fairchild researchers begin annual monitoring of tree cactus populations in the Keys, working with local land managers. They note early signs of stress from rising salinity.
• 2011: King tides bring saltwater flooding to the cactus’s habitat, increasing soil salinity and stressing the plants.
• 2015: A major herbivory event devastates the population, reducing it from 150 to 60 stems. Researchers suspect freshwater scarcity drove mammals to eat the cacti.
• 2016: The population drops further to 28 rooted stems, a 50% decline from the previous year. Saltwater intrusion and soil erosion continue to take their toll.
• 2017: Hurricane Irma hits Key Largo with a 5-foot storm surge, flooding the habitat for days and accelerating soil depletion.
• 2019: King tides flood the area for three months, leaving the cactus’s habitat submerged in saltwater. Only a handful of stems remain.
• 2021: Just six ailing stems are left. Researchers salvage them for off-site cultivation, effectively ending the cactus’s natural presence in the U.S.
• 2022–2023: Field surveys find no naturally growing Key Largo tree cacti. In 2023, a small, regrown fragment is spotted but deemed non-viable. The species is declared locally extinct.

This timeline, drawn from a study published in the Journal of the Botanical Research Institute of Texas in July 2024, paints a stark picture of a species overwhelmed by cascading environmental pressures.

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A Bellwether for Coastal Ecosystems

The extinction of the Key Largo tree cactus is more than a local tragedy—it’s a warning sign for other low-lying coastal species. Jennifer Possley, lead author of the study and director of regional conservation at Fairchild Tropical Botanic Garden, called it a “bellwether for how other low-lying coastal plants will respond to climate change.” 

The Florida Keys, with their low elevation and proximity to the sea, are a microcosm of the challenges facing coastal ecosystems worldwide.

The cactus’s habitat—a narrow fringe between mangroves and upland hammocks known as thorn scrub—is disappearing. Rising seas and storm surges are eroding these delicate ecosystems, leaving little room for species like the Key Largo tree cactus to adapt. 

Unlike some plants that can migrate to higher ground, the cactus was trapped on its limestone outcrop, surrounded by unsuitable mangrove substrate. This lack of dispersal options made it particularly vulnerable.

The Key tree cactus (Pilosocereus robinii), a federally endangered species, faces similar threats. Listed as endangered in 1984, its population dropped by 84% between 1994 and 2007 due to habitat loss, over-collection, and invasive species. 

Botanist John Small noted in 1917 that the Key tree cactus, once abundant in Key West, was nearing extinction due to deforestation and development. The parallels with the Key Largo tree cactus are chilling—both species are victims of human-driven changes to their environment.

Other coastal species in the Keys are at risk too. The endangered Key Largo woodrat and silver rice rat have been forced to higher elevations as seas rise, but suitable habitat is shrinking.

A 1976 study by University of Miami researcher Taylor Alexander linked the loss of slash pines on Key Largo to rising soil salinity, a fate that echoes the cactus’s demise. 

The Center for Biological Diversity identified 233 federally protected species in 23 coastal states as at-risk from sea level rise, underscoring the broader threat to biodiversity.

The Human Factor: Climate Change and Beyond

The extinction of the Key Largo tree cactus is a direct consequence of human-driven climate change. Burning fossil fuels, deforestation, and industrial activities have increased greenhouse gas emissions, warming the planet and accelerating sea level rise. 

The National Oceanic and Atmospheric Administration (NOAA) reports that sea levels in South Florida are rising at a rate of 3–4 millimeters per year, with Vaca Key (south of Key Largo) seeing a rise of 1.38 feet per century.

A 2022 NOAA report predicts U.S. sea levels will rise 10–12 inches by 2050, putting more species at risk.

But climate change isn’t the only human impact. Development in the Florida Keys has destroyed habitats for decades. The Key tree cactus, once common, was decimated by logging and land clearing for tourism and housing. 

Over-collection of rare plants and the introduction of invasive species have further stressed native flora. The Key Largo tree cactus, discovered in an isolated mangrove forest, was spared some of these pressures initially, but it couldn’t escape the rising seas.

Conservation Efforts: A Glimmer of Hope

Despite its extinction in the wild, the Key Largo tree cactus isn’t gone entirely. In 2021, researchers salvaged the last six stems and took them to Fairchild Tropical Botanic Garden and John Pennekamp Coral Reef State Park for cultivation. 

Today, about 60 specimens are grown in nurseries, and over 1,000 seeds are stored in seed banks at Fairchild and the U.S. Department of Agriculture’s National Seed Bank in Colorado. These efforts offer a lifeline for the species.

There are tentative plans to reintroduce the cactus to the wild, but finding suitable habitat is a challenge. The ideal location would need to be at a higher elevation, safe from king tides and storm surges, with the right soil and sunlight conditions. 

Jennifer Possley and her team are working with the Florida Department of Environmental Protection to identify potential sites, but they acknowledge that this may be a temporary solution. As seas continue to rise, suitable habitats are shrinking.

Conservationists have also learned from the Key tree cactus, which has been sustained through similar reintroduction efforts. Potted cacti are grown in Coral Gables, and seeds are banked for long-term preservation.

These measures can’t reverse the loss of the Key Largo tree cactus in the wild, but they provide hope for its survival in cultivation.

Why This Matters: A Wake-Up Call

The loss of the Key Largo tree cactus is a stark reminder of the cascading effects of climate change. It’s not just about one species—it’s about the ecosystems that depend on it. The cactus provided food and habitat for bats, birds, and mammals, and its extinction disrupts those relationships. 

As George Gann, executive director of the Institute for Regional Conservation, noted, “We are on the front lines of biodiversity loss.”

Over the past 25 years, more than one in four native plant species in South Florida have faced regional extinction or severe threats, with over 50 species already gone, including four global extinctions.

This extinction also raises questions about the future. How many more species will follow the Key Largo tree cactus? What happens when entire ecosystems, like the thorn scrub or mangroves, disappear? 

The Florida Keys are a preview of what could happen in other low-lying coastal regions, from Bangladesh to the Pacific Islands. The stakes are high, and the need for action is urgent.

What Can Be Done?

The extinction of the Key Largo tree cactus underscores the need for proactive conservation and climate action. Here are some steps that could help protect other vulnerable species:

1. Reduce Greenhouse Gas Emissions: Cutting carbon emissions through renewable energy, energy efficiency, and sustainable practices can slow sea level rise and give ecosystems a chance to adapt.
2. Protect and Restore Habitats: Preserving coastal habitats like mangroves and thorn scrub is critical. Restoration projects can help rebuild soil and create buffers against rising seas.
3. Support Conservation Programs: Seed banks, nurseries, and reintroduction efforts are vital for saving endangered species. Public funding and private donations can bolster these programs.
4. Raise Awareness: Educating communities about the impacts of climate change can drive grassroots action. The loss of the Key Largo tree cactus is a powerful story to share.
5. Monitor and Research: Continued monitoring of at-risk species, like the Key tree cactus and Key Largo woodrat, can help scientists intervene before it’s too late.

Why the Key Largo Tree Cactus Matters

For those who never saw the Key Largo tree cactus in its prime, it’s hard to grasp its majesty. Imagine a towering cactus, its white flowers glowing under the moon, bats flitting around it in the night. Picture its reddish-purple fruits, a feast for wildlife in a harsh environment. 

This wasn’t just a plant—it was a symbol of the Florida Keys’ unique beauty and resilience.

Its loss feels personal to many. James Lange, a botanist who monitored the cactus for years, described the moment he realized it was doomed: “Everything was just looking horrible. We knew there was no long-term hope for this population.” 

For plant physiologist Lewis Ziska, who admired the cactus during visits to the Keys, its extinction brought “a sense of loss, almost a mourning.” These emotions resonate with anyone who cares about the natural world.

The Key Largo tree cactus may be gone from the U.S., but its story isn’t over. It’s a call to action—a reminder that we can still fight for the species and ecosystems that remain. By learning from this loss, we can work to prevent the next one.

The Bigger Picture: Climate Change and Biodiversity

The extinction of the Key Largo tree cactus is part of a larger crisis. Globally, climate change is driving species toward extinction at an alarming rate. The Intergovernmental Panel on Climate Change (IPCC) estimates that 20–30% of species could face extinction if global temperatures rise by 2°C above pre-industrial levels. 

Coastal ecosystems, like those in the Florida Keys, are particularly vulnerable due to their low elevation and exposure to rising seas.

In South Florida, the stakes are especially high. The region is a biodiversity hotspot, home to unique species found nowhere else. But habitat loss, invasive species, and climate change are taking a toll. 

The Key Largo tree cactus is just one casualty in a region where over 25% of native plants are threatened. Other species, like the Key Largo woodrat, silver rice rat, and Big Pine partridge pea, are on the brink. Without action, the Keys could lose much of their natural heritage.

Looking Ahead: Can We Save the Next Species?

The story of the Key Largo tree cactus is a tragedy, but it’s also an opportunity. Its extinction has given scientists valuable insights into how climate change affects coastal species. By studying its decline, researchers can better predict and mitigate threats to other plants and animals. 

The conservation efforts underway—nurseries, seed banks, and reintroduction plans—show that there’s still hope, even in the face of loss.

But hope alone isn’t enough. Addressing climate change requires global cooperation, from reducing emissions to protecting vulnerable ecosystems. The Key Largo tree cactus may be a bellwether, but it doesn’t have to be a death knell. 

By acting now, we can honor its legacy and protect the countless species still fighting to survive.

Final thoughts: A Legacy of Loss and Lessons

The Key Largo tree cactus was more than a plant—it was a piece of Florida’s soul, a testament to the beauty and fragility of the natural world. Its extinction in the U.S., driven by rising sea levels, hurricanes, and herbivory, marks a sobering milestone. It’s the first species lost to sea level rise in the U.S., but it won’t be the last unless we act.

This cactus’s story is a wake-up call. It reminds us that climate change isn’t a distant threat—it’s happening now, reshaping ecosystems and erasing species. But it also shows the power of human ingenuity and determination. Through conservation, research, and collective action, we can prevent other species from meeting the same fate.

The Key Largo tree cactus may no longer grow in the wild in the U.S., but its seeds and cultivated plants carry its legacy forward. Let’s use that legacy to inspire change, protect biodiversity, and ensure that the Florida Keys—and the world—remain vibrant with life.

References

1. Possley, J., et al. (2024). Journal of the Botanical Research Institute of Texas. Link
2. Florida Museum of Natural History. (2024). “First local extinction in the US due to sea level rise.” Link
3. ABC News. (2024). “Key Largo tree cactus becomes 1st-ever US species to become extinct due to rising sea levels.” Link
4. The Guardian. (2024). “Florida: tree cactus becomes first local species killed off by sea-level rise.” Link
5. EcoWatch. (2024). “Key Largo Tree Cactus Is First Florida Species to Become Locally Extinct Due to Climate Change.” Link
6. Scientific American. (2024). “First U.S. Species to Go Extinct from Rising Seas Is the Key Largo Tree Cactus.” Link
7. The Washington Post. (2024). “Tree cactus is first of its kind to go extinct in U.S. from sea-level rise.” Link
8. Miami Herald. (2024). “Sea rise drives first species locally extinct in Florida Keys.” Link
9. NOAA. (2022). “2022 Sea Level Rise Technical Report.” Link
10. Center for Biological Diversity. (2013). “233 Species at Risk from Sea Level Rise.” Link