When Aaron Lee embarked on his Ph.D., he figured he would spend most of his time behind a computer analyzing existing data. He never expected to find himself analyzing historic plant specimens in the University of Minnesota Herbarium at the Bell Museum, some dating back to the 19th century, or venturing into the field to collect plants for “ground truthing” purposes.
That shift in perspective was sparked by a collaboration between his advisor, Plant and Microbial Biology Associate Professor Ya Yang, and ASCEND, an NSF-funded spectral biology collaboration led by Dr. Jeannine Cavender-Bares, previously based at the University of Minnesota. Using spectroscopy — a tool more commonly associated with satellite remote sensing — Lee realized he could uncover a trove of hidden data within the Bell Museum’s Herbarium.
Scanning the past for clues in the present
Working with Yang, who is curator of the Herbarium, and Tim Whitfeld, the collections manager, Lee gained access to a resource of nearly one million specimens, about a third of them from Minnesota. While the collection spans 150 countries, Lee focused closer to home. He identified specimens collected around Minneapolis and St. Paul dating back to 1876, a time when the Twin Cities were still relatively rural.
"We wanted to see if these crusty, dried, old leaves could tell us similar things about plants at the landscape level," Lee says.
Bit by bit, he scanned thousands of specimens to measure carbon, nitrogen, aluminum and magnesium content, something that had never been attempted at this scale. By comparing these "chemical fingerprints" across 150 years of urban development, Lee could see how plants adapted as the landscape shifted from prairie and forest to a bustling metropolis.
Global evolution in real time
Lee’s work didn't stop in the archives. To ensure his data was accurate, he performed "ground-truthing" fieldwork across Colorado, California, Minnesota and Florida. This combination of old and new data allowed him to analyze over 1,500 specimens from the Buckwheat and Smartweed family (Polygonaceae).
His findings challenged old assumptions: plant function evolves in highly context-dependent ways on much shorter timescales than previously thought. It turns out that evolution doesn't always repeat itself, even when different lineages are facing the same environmental pressures.
"There's so much more to these herbarium specimens than just the record itself," says Lee. "There’s the human story around it, but also the biological story."
Infrastructure for the unknown
As Lee prepares to start a postdoctoral position in the Cavender-Bares lab at Harvard, he leaves with a profound respect for the "physical library" of the Herbarium.
"The cool thing about herbaria is you never know what the future will bring," Lee says. "Specimens may have been collected for a single purpose 100 years ago, but they become these dynamic, multi-purpose records for science that haven't even been invented yet."
Whitfeld agrees, noting that these specimens provide a tangible baseline for a changing world. "You have this sort of time machine," he says. "We don’t need to speculate about the past, because we can look at the specimen, which has a label and a date. It provides the perfect context for the present." –Stephanie Xenos