America lost its only Key Largo tree cactus in what scientists call our first local plant extinction caused by rising seas. Researchers monitored these rare cacti for years, watching as salt water, storms, and animal feeding destroyed what was once a thriving group of about 150 plants. By 2021, only six dying fragments remained, which scientists collected for growing in protected settings.
Key Largo tree cactus (Pilosocereus millspaughii) still grows on a few islands in Cuba and the Bahamas. Yet its disappearance from Florida sounds an alarm about what might happen to other coastal plants as climate change advances.
Identifying Key Largo Tree Cactus
Scientists discovered this rare cactus in 1992, hidden in a mangrove forest on Key Largo. Nobody knew exactly what kind of cactus they had found for many years. Most experts thought it was simply an unusual group of Key tree cactus (Pilosocereus robinii), which grows elsewhere in the Florida Keys and is federally endangered.
Both cacti grow tall and straight, reaching over 20 feet. Each produces cream-colored flowers with a garlic scent that glows under moonlight to attract bats for pollination. Both also produce bright red and purple fruits that birds and mammals enjoy eating.
Alan Franck, now working as herbarium collection manager at the Florida Museum of Natural History, noticed key differences that suggested something new. Most striking was a thick tuft of woolly hairs at flower and fruit bases, sometimes resembling snow covering parts of each cactus. Franck also found that spines on Key Largo specimens grew twice as long as those on Key tree cactus.
After careful study, Franck confirmed in 2019 that scientists had found Pilosocereus millspaughii, marking its first and only known appearance in the United States. Sadly, by then, rising seas and other pressures had already begun destroying this unique population.
CAUSES OF EXTINCTION
Multiple factors combined drove Key Largo tree cactus to extinction on US soil. Each threat alone might have allowed some plants to survive, but they created impossible conditions for these rare cacti together.
Salt Water Intrusion From Rising Seas
Rising sea levels gradually pushed salt water into the soil around the Key Largo tree cactus habitat. Studies conducted by Fairchild botanists showed higher salt levels in the soil beneath dead cacti than in living ones, particularly after storm surge events. Salt-tolerant plants from mangrove areas began growing on limestone outcrops where cacti lived, a clear sign that increasing salinity was killing freshwater plants.
Soil Erosion From Hurricanes and High Tides
Key Largo tree cacti grew on low limestone outcrops surrounded by mangroves near the shore. Initially, a layer of soil and organic matter covered these rocks, allowing cacti to root and grow. Hurricane storm surges and unusually high “king tides” gradually washed away this vital soil layer until almost nothing remained. Without soil, cacti lost nutrients and anchoring needed for survival.
Mammal Herbivory Damaging Remaining Plants
In 2015, researchers discovered an alarming problem: Half of the cacti had died from animal feeding damage. When fresh water becomes scarce, animals often target cacti for the water stored in their stems. In 2011, king tides flooded areas with salt water, possibly driving mammals to seek water from cacti when other sources vanished. Scientists set up cameras to identify culprits, but damage patterns changed after the initial attacks.
Timeline of Decline
Scientists first found the Key Largo tree cactus in 1992, marking a significant botanical discovery for Florida. After initial identification, monitoring began sporadically, with researchers periodically visiting to check population health.
A major crisis struck in 2015 when research teams arrived for a routine assessment. Half of all cacti had died from severe animal feeding damage. Cacti store water in their stems, making them attractive targets during dry periods or when freshwater becomes scarce. Researchers installed cameras hoping to identify culprits, but whatever animals caused the damage never returned.
Surprisingly, when scientists returned in 2016, approximately half of the remaining plants had died despite no evidence of continued herbivory. Responding to the rapid decline, Fairchild and the Florida Department of Environmental Protection staff collected cuttings to grow in protected greenhouse settings.
Hurricane Irma, a category five storm, devastated the Florida Keys in 2017, creating massive flooding across Key Largo. The storm surge reached 5 feet high, and many areas remained underwater for days afterward. Recovery teams conducted emergency work with several cactus populations throughout the Keys, removing fallen branches and salvaging damaged plants. Conditions grew so extreme that biologists provided kiddie pools filled with fresh water to help local wildlife survive.
King tides 2019 brought more destruction, flooding large sections of Key Largo for over three months. Low-lying areas where cacti grew remained completely submerged, further degrading already compromised habitat.
By 2021, only six stems remained alive in the wild. Scientists allowed these final plants to flower and produce fruit for one last season before collecting all remaining living material for cultivation in controlled environments. With this final collection, Key Largo tree cactus became officially extinct in wild American landscapes.
Conservation Efforts
Researchers mounted emergency salvage operations as the number of Key Largo tree cactus dwindled. After watching population declines accelerate, Fairchild Tropical Botanic Garden staff collected cuttings from the remaining plants in 2016 to grow safely in greenhouses.
Following the final population collapse in 2021, scientists harvested all remaining wild material. Growing conditions at Fairchild facilities in Coral Gables allow cacti to thrive away from saltwater intrusion, flooding, and animal damage. Current cultivation includes both potted plants and outdoor specimens in carefully managed settings.
Fairchild botanists implemented robust seed banking programs for long-term preservation. Seeds collected from wild plants and cultivated specimens rest in secure storage facilities. Banking genetic material from different individuals helps maintain diversity within conservation collections, preserving options for future recovery work.
Potential reintroduction remains on the agenda despite challenges. Jennifer Possley noted, “We have tentative plans with the Florida Department of Environmental Protection to replant some in the wild.” Similar efforts already support the survival of related Key tree cactus, where reintroduced plants now outnumber naturally occurring specimens.
Finding a suitable habitat poses major obstacles to any reintroduction effort. Key Largo tree cactus requires specific growing conditions, which botanists call “thorn scrub” areas between mangroves and upland hammocks. As sea levels rise, these narrow transition zones vanish, leaving fewer places where replanted cacti might survive independently.
Related Species Facing Similar Threats
Key tree cactus (Pilosocereus robinii), a close relative of Key Largo tree cactus, faces many identical challenges to survival. Both species share similar growth patterns and habitat requirements, making them equally vulnerable to rising seas and habitat loss.
Historical records paint a stark contrast to current reality. Botanist John Small wrote in 1917 that Key tree cactus “was for a long time very abundant” throughout Key West and surrounding areas. Small documented how development and wood harvesting pushed populations toward collapse, noting even then that this “interesting cactus has become scarce, until at present it is on verge of extermination in its natural habitat.”
Federal protection came too late to prevent major declines. Government agencies listed Key tree cactus as endangered in 1984, but numbers continued falling dramatically. Between 1994 and 2007, population surveys documented an alarming 84% decrease in wild plants.
Annual monitoring began in 2007 when Fairchild researchers partnered with land managers to track all remaining tree cactus populations. Their studies confirmed salt levels rose significantly in soil beneath dead cacti following storm surge events, proving direct links between increased salinity and cactus mortality.
Reintroduction programs now serve as lifelines for dwindling populations. Fairchild-led projects have successfully planted greenhouse-grown cacti back into protected areas. Possley notes these efforts have been so extensive that “reintroduced material of this species is already more than amount of wild material that’s left.” Without these human interventions, Key tree cactus might already share fate of its Key Largo cousin.
Habitat Disappearance Limits Replanting Success
Finding places to reestablish Key Largo tree cactus becomes increasingly tricky as coastal habitats transform. Plants need specific growing conditions in narrow zones called “thorn scrub,” transitional areas between mangrove swamps and higher-elevation hammock forests.
Rising seas steadily shrink these crucial habitat zones. As saltwater pushes inland, mangroves migrate toward higher ground, squeezing out specialized plant communities that once thrived between ecosystem boundaries. Land managers struggle to identify protected areas with suitable conditions for cacti reintroduction.
Soil salinity levels continue climbing in remaining habitat fragments. Studies conducted by Fairchild researchers demonstrate clear connections between salt concentration and cactus mortality. Even areas that appear suitable based on elevation may contain too salty soil for long-term plant survival.
Limited options exist for sustainable replanting programs. Conservation lands face multiple pressures from development, invasive species, and changing climate conditions. Without addressing the root causes of habitat loss, reintroduction efforts may provide temporary solutions rather than permanent recovery for endangered plants.
Warning Signs for Coastal Plant Communities
Key Largo tree cactus extinction is an early warning for what many coastal plants will face in the coming decades. Jennifer Possley describes it as “a bellwether for how other low-lying coastal plants will respond to climate change,” – offering a glimpse into future challenges for conservation.
Multiple climate impacts combine to accelerate species decline. Rather than simple, predictable sea level rise, plants face complex combinations of threats, including storm surges, extended flooding periods, saltwater intrusion, soil erosion, and changing rainfall patterns. Hurricane Irma demonstrated how single weather events can devastate already stressed populations.
According to George Gann, executive director of the Institute for Regional Conservation, South Florida biodiversity faces unprecedented risk: “We are on the front lines of biodiversity loss,” “Our research in South Florida over the past 25 years shows that more than one-in-four native plant species are critically threatened with regional extinction or are already extirpated due to habitat loss, over collecting, invasive species and other drivers of degradation. More than 50 are already gone, including four global extinctions.” He said.
Growing evidence suggests current losses represent the beginning of a larger biodiversity crisis. Gann reports “more than 50 [species] are already gone, including four global extinctions” from South Florida ecosystems. As scientists document these changes, Key Largo tree cactus joins the growing list of species unable to adapt quickly enough to rapidly changing coastal environments.
Lessons From a Lost Cactus
Active monitoring provided valuable data about how multiple environmental factors interact during population collapse. Future conservation programs should implement similar long-term tracking systems for vulnerable coastal species before crisis points are reached.
Successful preservation requires anticipating habitat changes rather than simply responding to them. Forward-looking conservation must identify and protect land at higher elevations where coastal plants might migrate naturally as seas rise.
Collaboration between researchers, land managers, and government agencies proved crucial during the decline of the Key Largo tree cactus. Fairchild botanists, Florida Department of Environmental Protection staff, and other partners worked across organizational boundaries to document changes and preserve genetic material.
Funding for plant conservation lags behind support for more visible endangered animals. Redirecting resources toward botanical conservation could prevent additional plant extinctions while maintaining ecosystem function.
Many solutions already exist but need wider implementation. Protected corridors allowing plant migration, assisted relocation programs, genetic preservation, and habitat restoration all offer pathways for conservation – if properly supported and funded.
Local communities can participate in saving rare plants through citizen science programs, habitat protection on private land, and carbon footprint reductions. Fighting climate change requires global policy changes and individual actions working together toward common goals.
