How can closely related plant species occur on two continents, thousands of miles apart? This distribution pattern is known as disjunction, and it’s a particular area of interest for Dr. Jun Wen, an evolutionary botanist at the Smithsonian’s National Museum of Natural History.

Back in China, Wen’s grandfather was a traditional Chinese medicine doctor in her home village. Wen showed early interests and talent in medicinal herbs, but as the daughter—and furthermore as the doctor’s daughter’s daughter—she was never considered to take over the family business. “I am two places wrong,” Wen laughed. Yet, her enthusiasm for plants led her to becoming a successful botanist and evolutionary biologist—and, luckily for us, a ginseng expert.

Among other species, Wen and her research associates have carefully studied Asian ginseng (Panax ginseng), naturally occurring along the border of China, Russia, and North Korea, and American ginseng (Panax quinquefolius), found in the wild in the Appalachian Mountains of North America. Their goal: to unlock the mysteries of their disjunction.

Working with ginseng species since the 1990s, Wen uses such tools as living plants, preserved specimens, DNA samples, distribution information, and software and computer programs. She has analyzed 356 samples of ginseng from 47 populations collected across its entire distributional range. Her method for each has been the same: she pinches off a small piece of leaf from every sample and extracts the same DNA sequences from them. Then she lets the machines and computer do their work.

DNA is like the record of our life and our history; it inherits and preserves genetic information from the previous generations but also gradually changes through the following generations. By tracing these changes, Wen can calculate the evolutionary trajectory of the DNA sequences—which is essentially the evolutionary trajectory of the species. A computer program clusters the DNA sequences according to their similarity and dissimilarity, and finally it constructs a family tree of these ginsengs—a phylogeny. From there, the relationship among ginseng species is clear to Wen. She can tell which ones derived earlier and which were the descendants.

But how did these two plants settle at opposite sides of the globe? By mapping the current distribution of each sample on the phylogeny, a computer can simulate the most likely scenarios of ginseng’s dispersal patterns. What also intrigued Wen was the timing of the disjunction. For this, the whole phylogeny was “calibrated” with some certain dates inferred from fossils. Thus the timescale for ginseng species’ diversification events could be computed. Finally, by piecing all this information together, Wen has been able to reconstruct what happened in the past, where, and when.

With the current results and evidence, her conclusion is that the ancestor of American ginseng left its Asian kin and dispersed at approximately 14.65 Ma (million years before present) across the Bering Bridge, a land route connecting present-day Russia and Alaska that formed when sea levels dropped and inland seas shrank during 24-5.3 Ma. Different ginseng species then evolved on the two separate lands.

Imagine you are a ginseng seed that goes for a ride along with a migration of animals from one continent to another. Where would you look for a new home? It makes sense that the seed would thrive in an environment similar to its original habitat. Originally, those ginseng plants grew in temperate Asia under thick deciduous forest. After the long travel and surviving the tumultuous climate in the subsequent millions of years, it took root in the mountains and forests across eastern North America.

The study of ginseng has not ended. Wen is still collecting samples across ginseng’s natural habitats on both continents. Employing cutting-edge techniques in her study, Wen hopes to elaborate on the evolutionary story of ginseng.

“This is the right time for doing such research,” she explained. “We can obtain thousands of genes at once. This massive amount of data can be used to answer the evolutionary questions that were impossible to address just a few years ago.” 

While Wen’s research proves it, the evolutionary and geographic journey of ginseng was theorized long before. In 1716, after a three-month search, Jesuit missionary Joseph-François Lafitau found wild American ginseng in Canada with the help of the indigenous people who also used it as a medicinal herb. As an ethnographer devoted to the study of Native North Americans, he hypothesized that indigenous peoples of the region originally migrated from Asia. Recognizing the uncanny resemblance of the two ginseng plants from two ends of the world—both in appearance and human applications—Lafitau believed ginseng would be the perfect evidence of his theory.

This human migration was later substantiated, although it happened around 15,000 years ago—millions of years after ginseng made its journey. In fact, ginseng dispersed millions of years before humans even existed.

Human activity didn’t affect ginseng’s ancient migration, but it definitely launched its modern migration—from North America back to Asia. Upon the identification of American ginseng, Lafitau also involuntarily set in motion a global commerce opportunity. Since then, the trade of the plant’s roots between North America and Asia has been a thriving business. Nearly all harvested wild American ginseng is exported to China, Hong Kong, or Taiwan, where the root is strongly tied to the culture and has been held in great esteem for its mysterious efficacy in traditional Chinese medicine for centuries.

Whether driven by nature or by people, the migration of ginseng is fascinating and significant—not only biologically but also culturally. The journey of ginseng has bridged the oldest and the youngest empires bound by the Pacific Ocean, connecting the natural history and human knowledge of the Eastern and Western worlds.

Shirly Hsuan Chang is a research intern at the Center for Folklife and Cultural Heritage with the American ginseng project. With a background in botany, she brings a more scientific perspective to the project.

References

Zuo, Y.J., J. Wen and S.L. Zhou. “Intercontinental and intracontinental biogeography of the eastern Asian – Eastern North American disjunct Panax (the ginseng genus, Araliaceae), emphasizing its diversification processes in eastern Asia.” Molecular Phylogenetics and Evolution 117 (2017): 60-74.

Wen, J., Z.L. Nie and S.M Ickert-Bond. “Intercontinental disjunctions between eastern Asia and western North America in vascular plants highlight the biogeographic importance of the Bering land bridge from late Cretaceous to Neogene.” Journal of Systematics Evolution 54 (2016): 469–490.

Lee, C., J. and Wen J. “Phylogeny of Panax using chloroplast trnC-trnD intergenic region and the utility of trnC-trnD in interspecific studies of plants.” Molecular Phylogenetics and Evolution 31 (2004): 894–903.