Scrub Lupine Lupinus cumulicolaPhoto by: Christine Sit

How evolution put the flora in Florida

Author: Aaron David

The Lake Wales Ridge is an ancient sand dune ridge that extends through Highlands and Polk counties and is home to nearly two dozen plant species found nowhere else on earth. Yet our incredible diversity of flora is just one sliver of the much larger biodiversity hotspot that encompasses the entire Southeastern Coastal Plain that spans the coastal regions of Texas to the Carolinas. In Florida, the landscape has endured periods of inundation as glaciers came and went, and the corresponding sea level rose and fell, with the most recent period of inundation occurring roughly 125 thousand years ago. These climate patterns caused the ‘temporary’ formation of sand islands like the Lake Wales Ridge, and subsequent re-connection of the Florida landmass as sea level fell over the course of thousands of years, until our present-day coastline was formed.

“These conditions were ripe for what evolutionary biologists call ‘speciation’, or the evolution of new species,” said Dr. Aaron David, Director of Plant Ecology at Archbold Biological Station. Speciation often occurs when two populations of a species are geographically isolated, such as when sea level rise divides a population onto two different islands. Populations will slowly become increasingly different from one another over thousands or millions of years. When the species eventually come back into contact, such as when sea level recedes, the hybridized offspring of the two new species struggle to survive, further cementing the two populations as new, distinct species. The result is many closely related but unique species found across the ridges and high elevation habitats throughout the Southeastern Coastal Plain.

In recent years, evolutionary biologists have teamed up with taxonomists (scientists really good at species identification) to describe a slew of new species in Florida. For example, several new species of lupines were recently described based on their physical attributes and genetics. From that study, we learned that our local skyblue Scrub Lupine (Lupinus cumulicola) is, in fact, unique to the Lake Wales Ridge. In another study, a plant species called Bluecurls, which is arguably the most beautiful bloom found in the scrub, was divided into several species, including yet another species found only on the Lake Wales Ridge (Trichostema bridgesii-orzellii).

“One of the amazing things we have learned from this work is just how quickly speciation in Florida occurred – many of these species evolved over the course of tens of thousands of years, rather than the more usual hundreds of thousands or millions of years. In evolutionary time, speciation of Florida’s flora was lightning fast!” said Dr. Sterling Herron, a Research Assistant in Archbold’s Plant Ecology Program.

Furthermore, we’ve learned a great deal about the evolution of our endemic plants. For example, there are roughly a dozen species of Dicerandra mints in the southeast, many of which are limited to single counties in Florida. In Highlands County, we are lucky enough to have two species – one restricted to Lake Placid and Venus (Scrub Mint, Dicerandra frutescens), and the other (Garrett’s Mint, Dicerandra christmanii) restricted to Sebring and Avon Park. Despite these tiny, nearby ranges, these two species aren’t even all that closely related. In fact, Scrub Mint is more closely related to species restricted to Lake Wales, Titusville, and Vero Beach than it is Garrett’s Mint. David said, “The evolutionary history of the Dicerandra mints must have included a meandering journey around Florida as sea level rose and fell.”

Dicerandra side by sidePhoto by: Reed Bowman (left) & Christine Sit (right)

Caption: Scrub Mint (Dicerandra frutescens) and Garrett’s Mint (D. christmanii) are both restricted to the Lake Wales Ridge, but are not as closely related as one might think. Photos by Reed Bowman (left) and Christine Sit (right).

So, why does it matter whether we call an organism a single species or several species? First, by recognizing that we have more species than previously believed, we gain a deeper understanding of the wonderful diversity we have. Second, many of these newly described species have incredibly narrow geographic ranges of only a few counties and may be eligible for state or federal listing as endangered. Third, unraveling these speciation secrets is simply an important part of the natural history of our region, and gives us an appreciation of the nature around us.

David concluded, “The Lake Wales Ridge right here in Highlands County plays a critical role in helping uncover the mysteries of plant evolution.”

Main photo caption: Scrub Lupine (Lupinus cumulicola) was recently learned to be restricted to the Lake Wales Ridge. Photo by Christine Sit.