Everglades Bully: How a Microscope Found a Threatened Shrub Hiding in Plain Sight

Where pineland meets prairie in Big Cypress National Preserve, southwestern Florida: the kind of transitional ground where Everglades bully grows. NPS/Erick Revuelta.

The National Park Service works to keep rare plants and animals from disappearing, and Big Cypress National Preserve, about 729,000 acres of freshwater swamp in southwestern Florida, shelters many of them. One is Everglades bully (Sideroxylon reclinatum subsp. austrofloridense), a thorny shrub 3 to 6 feet tall with oval evergreen leaves and clusters of small white flowers. It grows only in southern Florida, was first found in the preserve in 2002, and was listed as threatened under the Endangered Species Act in 2017.

Its protection turned out to depend on a scanning electron microscope.

Two look-alike cousins

The species has two subspecies. Everglades bully lives in only three counties — Collier, Miami-Dade and Monroe — usually where pine rockland meets marl prairie, and also grows in Everglades National Park. Its cousin, Florida bully, is widespread across Florida and neighbouring coastal states.

Elsewhere they are easy to tell apart: Everglades bully has fuzzy undersides to its leaves, Florida bully does not. But in Big Cypress, you cannot reliably tell them apart by eye. How can managers protect a plant they cannot identify?

Sideroxylon reclinatum blooming in Big Cypress. Leaves without fuzz usually mean Florida bully — but not here. NPS/Erick Revuelta.

Researchers found Everglades bully in the preserve in 2002. A decade later, surveyors struggled to tell the subspecies apart, finding many plants with in-between fuzziness. Then in 2014 other researchers showed that the two could be reliably separated by looking at the underside of a leaf through a high-powered microscope. In Everglades bully, the cells of the leaf's outer skin have visible grooves, like a turtle's shell; in Florida bully, there are only raised ridges on an otherwise smooth surface, like crinkled aluminium foil.

What the microscope showed

In 2022, working with Fairchild Tropical Botanic Garden, whose botanists led the fieldwork and microscopy, the Park Service combined field surveys with electron microscopy in the preserve for the first time. The team recorded about 250 locations of the plant and took leaf samples from nearly 100 individuals.

Every plant looked like the common subspecies to the naked eye. Under the microscope, at least 85 percent were the threatened Everglades bully, and only 15 percent Florida bully. The rare plant also turned up more than 10 miles from anywhere it had been known before, and several populations were mixed, the two subspecies sometimes just feet apart.

Why it matters

The findings are being built into project planning across the preserve, and may support the U.S. Fish and Wildlife Service in designating critical habitat for the subspecies. Everglades bully was listed because of habitat loss to development and farming, poor fire management, invasive plants, hurricanes and wildfires, and sea level rise; in Big Cypress it also faces off-road vehicles and altered fire and water patterns.

A question remains: why do the two look so alike where their ranges overlap? Perhaps the plants here evolved the microscopic leaf features before the fuzz, or perhaps the two subspecies are interbreeding at the edges of their ranges. Subspecies can cross and produce fertile offspring. It may be evolution in progress.

Sources

• National Park Service, "Rare Plant and High-tech Microscope: A Surprising Conservation Story," Big Cypress National Preserve; rewritten in hubnx's own words. Based on J. Lange, C. L. Angelo, E. Revuelta and J. Possley, "Population Assessments of Federally Threatened Everglades Bully in Big Cypress National Preserve," Plants. Photographs by the National Park Service; images credited to the botanic garden and the university are left out.