Meet the Smithsonian Scientist Untangling the Branches of Hawaii’s Evolutionary Tree

From fragile ferns to towering trees, NMNH botanist Warren Wagner has spent over 30 years researching plants from the dense forests of the Pacific Islands.

A man wearing a ripped white shirt stands among thick greenery, holding a plastic sample bag
Warren Wagner, curator of Pacific botany at the National Museum of Natural History, ripped his shirt sleeve while collecting samples for the U.S. National Herbarium in the forest of West Maui with his colleague Vicki Funk.   Vicki Funk and Warren Wagner, NMNH

Warren Wagner seemingly has a story for every plant specimen in the National Museum of Natural History’s National Herbarium.  As he leafs through hundreds of pages plastered with dried Pacific Island plants, he recalls past botanical discoveries and far-flung expeditions.  A vibrantly colored violet brings to mind a 30-day sailing trip from Honolulu to the remote Marquesas Islands where he collected dozens of species that were entirely new to science.  A delicate evening primrose elicits a laugh from Wagner as he mentions that he named the new species after his wife.

As one of the world’s leading experts on Hawaiian flora, Wagner has spent his career detangling the endless web of evolutionary relationships that crisscross the Pacific Islands.  His research has led to 125 new species descriptions, nearly 250 scholarly articles and six books. After examining these plants for three decades, Wagner can pinpoint microscopic differences between related species and complex botanical diversification patterns with unparalleled accuracy.  

Wagner’s impressive contributions to plant systematics, evolution and biogeography have led him to serve as the president of the American Society of Plant Taxonomists and yielded prestigious honors such as the Asa Gray Botanical Award and the museum’s Scientific Achievement Award.

For the latest installment of Meet a SI-entist, Smithsonian Voices spoke with Wagner to learn where his plant passion first bloomed, what he thinks of the recent Maui wildfires, and how Hawaii’s volcanic history has shaped local botany.

Warren Wagner (left) and botanist David Lorence (right) on the sailboat of retired Coast Guard captain, Ed Carus, processing samples collected from the Marquesas Islands in 1988. Ed Carus

What sparked your interest in the field of botany?

Whenever I talk about my career, I always wonder, ‘how did a guy like me end up working on Pacific Island flora at the Smithsonian?’ because it definitely wasn’t planned.  I had wanted to be a chef, a mathematician, a computer scientist, and even a doctor.  But during my second year at the University of New Mexico, I came across a class called ‘Flora of New Mexico,’ and the description said, ‘includes field trips!’ I thought, cool, I love hiking and camping.  I signed up for the class, and to my surprise, my favorite part was memorizing all the characteristics of the different plant families.

I had always been interested in patterns and systems, and I realized that botany is full of plant patterns.  I knew the field was for me when I would go out hiking on the weekends, and I would come home with dozens of plants that I wanted to identify.  To me, this field has always felt like a big puzzle I wanted to solve, and I like to think I’ve helped put together at least a few of the pieces.  

How did you decide to focus your career on the Hawaiian Islands and Pacific botany?

After I finished my Ph.D., I came across a job opening in Hawaii at the Bishop Museum.  I had never been to Hawaii and had never wanted to go there.  I'm not a surfer.  But I was offered the job, so I bought a one-way ticket and never looked back.  It had been a hundred years since anybody had written a full summary of the plants of Hawaii, and I knew it was an important project that I wanted to tackle.  Although I had never studied Pacific Island plants, I was suddenly expected to be a botanical expert on this region, and I knew I needed to learn quickly.

After five years of research, Wagner and his co-authors published their 5,000-page manuscript in 1988 with descriptions of every known plant on the Hawaiian Islands.  The book contains the most comprehensive summary of Hawaiian flora to date. Warren Wagner, NMNH

It was a daunting project because botanical work is never really over.  Something is always changing.  Somebody discovers a new species or new research leads to a revised classification. That's just the nature of science. The second you decide you are done writing a book like this, it's out of date before you’ve even published it.  My book was always intended to be a snapshot of the plants growing on the islands at one point in time.  Rather than being greedy and keeping all the knowledge in my head while I continually added to the book forever, I wanted to take my snapshot and put it out there for everybody.  

What has been your biggest career highlight, something you feel has made an impact on the natural history world?

One of my interests in this field has always been implementing new technologies that help us conduct better research. In the past, plant taxonomy work was kind of intuitive. You would learn a lot of information and say, ‘well this pattern looks a bit like that, so these species must be related,’ and you would start to put together an evolutionary story.  But then researchers started doing chromosome work and chemical studies and created a formalized method for building computerized evolutionary trees that we now call cladistics.  

My colleague Vicki Funk and I became very interested in this new type of research, and we wanted to see if it could help answer one of the burning questions in Pacific Island science: do the evolutionary timelines of the organisms in Hawaii sync up with the ages of the different islands, from the formation of Kauai 5.1 million years ago to the Big Island less then 1 million years ago? 

We held a symposium and invited not only botanists but geologists, zoologists, and entomologists from around the world.  Together we wrote a book called, ‘Hawaiian Biogeography: Evolution on a Hot Spot Archipelago,’ and we were able to show that the way most plants and organisms colonized and diversified across the islands corresponds perfectly with the geologic record.  We discovered this without any intuition or storytelling, basing our conclusions solely on scientific data. 

Wagner holds Vol. 1 of the two-volume, “Flora of the Marquesas Islands,” which he co-authored with David Lorence.  During the collecting expeditions to these remote islands from 1988-2017, Wagner and collaborating botanists Ray FosbergMarie-Hélène Sachet and Jacques Florence increased the known native flora by 25%. Emma Saaty, NMNH

Are you worried that the recent Maui wildfires have destroyed rare or endangered plant species?

One of the most recent publications I helped write was about an endangered species of bellflower (Clermontia hanaulaensis) on Maui, so the fires have definitely weighed heavy on my mind.  These fires started with centuries of damage to the Hawaiian lowlands. When Europeans first came to Hawaii, they introduced invasive grasses that thrive with cycles of burning.  In recent years with the onset of climate change and wilder weather patterns including frequent droughts, fires have been increasing in frequency and intensity.  Each time plants are burned down, only the fire-adapted invasive plants are coming back.  Our worry is that over time, regions are becoming progressively less and less native until there are very few native species left. 

I know that sounds dire, but I still have a great deal of hope for these species.  In areas that are still more natural, restoration work is a constant priority.  Conservation staff have fenced in acres and acres of land where they are growing these rare and endangered species and protecting them from invasive plants and animals to give them a fighting chance at survival in the future.  These projects will be vital to the health of the islands going forward, because the more native biodiversity there is, the fewer fires there will be.  Conservation is a win-win for everyone!

"To me, this field has always felt like a big puzzle I wanted to solve, and I like to think I’ve helped put together at least a few of the pieces."  — Warren Wagner, NMNH curator of Pacific botany 

How does understanding the evolution and taxonomy of Pacific Island plants aid in conservation efforts?

When the Hibiscadelphus woodii was described by Wagner and Lorence in 1995, there were only four living representatives of the species in the world.  Now, thanks to drone expeditions launched by the National Tropical Botanical Garden, researchers are discovering new populations of endangered and presumed extinct species which will support conservation efforts in the future.  Emma Saaty, NMNH

I have found myself contributing to conservation throughout my entire career.  When the Endangered Species Act was passed in 1973, Hawaii was already considered one of the extinction capitals of the world.  The last summary of Hawaiian plant taxonomy had been published in 1888.  One hundred years later we published our book and delineated whether each species was vulnerable, rare, endangered, or likely extinct. The U.S. Fish and Wildlife Service adopted our classification of the status of each taxon and placed these plants on their rare and endangered species list, laying the framework for much of the conservation that goes on today.

A lot of people think that taxonomy work is just building an inventory list, but I always like to say it’s the pioneering exploration of life and the basis for countless other aspects of biological research.  Species names are the currency of diversity, and our research makes the vast and largely unused benefits of biodiversity accessible to humanity. Conservation work can’t happen until the classification research to which I have dedicated my career happens first and lays an essential foundation.

This conversation has been edited for length and clarity.

Meet a SI-entist: The Smithsonian is so much more than its world-renowned exhibits and artifacts. It is a hub of scientific exploration for hundreds of researchers from around the world. Once a month, we’ll introduce you to a Smithsonian Institution scientist (or SI-entist) and the fascinating work they do behind the scenes at the National Museum of Natural History.

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