Human influences on the ecology and evolution of medicinal plants: American ginseng as a case study
Restricted (Penn State Only)
- Author:
- Palkovitz, Rachel
- Graduate Program:
- Anthropology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 03, 2025
- Committee Members:
- Tim Ryan, Program Head/Chair
Tim Ryan, Major Field Member
Mary Shenk, Outside Field Member
George Perry, Chair & Dissertation Advisor
Eric Burkhart, Outside Unit Member - Keywords:
- Evolutionary Anthropology
American ginseng
medicinal plants
population genetics
phenotypic variation
unconscious selection
harvest-induced selection
conservation - Abstract:
- People utilize bioactive compounds in medicinal plants for traditional and biomedical healthcare practices around the world, a pattern that has been prevalent throughout human and non-human primate evolutionary history. Today, the herbal medicine market is a burgeoning industry exceeding USD 200 billion in annual sales, with herbal dietary supplements in the United States alone averaging over USD 13 billion annually. Growing demand for medicinal plants exceeds what is thought to be sustainable for wild-harvested medicinal plant species, many of which face conservation threats in their historical native habitat ranges. As a result, people cultivate medicinal plants on commercial scales to supply the global herbal medicine market. This dissertation examines potential human influences of harvesting and cultivation on medicinal plants from an evolutionary and anthropological perspective, using American ginseng as a focal case study. I employ a combination of molecular, phenotypic, and ethnobotanical methods to assess evolutionary change and contextualize human-plant interactions and their potential attendant mechanisms of selection. American ginseng (Panax quinquefolius L.), hereafter “ginseng,” is a shade-obligate understory perennial herb that occurs in the wild primarily in mesic forests of the eastern North America. Current evidence indicates ginseng has an allotetraploid genomic architecture that evolved from the combination of two diploid ancestor genomes and subsequent divergence from its tetraploid sister taxon, Panax ginseng (hereafter “Asian ginseng”), around 2.59 MYA. Ginseng plants contain bioactive saponin compounds called ginsenosides, which originally evolved as mechanisms of plant defense against pathogens and predators under natural selection in forest environments. Both American and Asian ginseng are highly valuable medicinal plants in Chinese Traditional Medicine: people use both species to treat a wide range of medical conditions. People have harvested ginseng from the wild for over hundreds of years, dating back to indigenous stewardship that continues today through descendent communities. Over the last 100 years, people have also been cultivating ginseng in forest farm or artificial shade gardens, which ginseng scientists hypothesize is a source of genetic variation via unconscious selection: changes in allele frequencies that rapidly accrue when plants are placed in a novel growing environment and reach maturity at faster rates than in the wild. In this work, I employ population genetics, digital morphometric phenotyping, and ethnobotanical key informant interviews with ginseng growers to assess genetic and phenotypic variation across modern and historical ginseng populations, testing two major hypotheses of human-mediated selection: wild-harvesting and unconscious selection via artificial shade cultivation. In chapter 1, I outline a framework for developing evolutionary anthropology research programs situated in local ecosystems within the United States—a model that evolutionary anthropologists can apply in any locality that is not traditionally within the purview of the field. Using ginseng as a primary example, I show how expanding beyond the typical foci of evolutionary anthropology (e.g. archaeological and fossil sites and subsistence economies) can advance broader evolutionary and ecological understanding of human-environment interactions and provide broader impacts in the communities we are a part of. In chapter 2, I assess geographic and putatively anthropogenic patterns of genetic structure and phenotypic diversity among modern ginseng plants in the U.S. and Canada by comparing individuals (N=566) from cultivated vs. wild-occurring populations from Wisconsin, Ontario, and Pennsylvania (N=41). I employ 14 microsatellite loci and five morphometric traits for a subset of individuals for which I collected both genetic and phenotypic data from high-resolution digital scans and measurements on live plants (N=140). I find preliminary evidence of genetic admixture between several cultivated and wild ginseng populations, where several wild populations have low genetic distance to artificial shade populations (Jaccard distance <0.2). I find that extensive genetic variation exists outside of cultivated populations, and identified several wild lineages, especially in southeastern Pennsylvania, that resource managers can prioritize for seed banking conservation efforts. Using Generalized Linear Models, I find that the artificial shade garden planting condition was a strong predictor of quantitative ginseng trait values for three traits: leaflet area, the proportion of marginal teeth, and the proportional length of the peduncle/inflorescence relative to the adjacent petioles. My analysis predicts that ginseng plants from artificial shade gardens will have larger leaflets, higher proportions of marginal teeth, and shorter peduncle-petiole ratios than their wild and forest farmed counterparts. Finally, I find through variance partitioning analysis that planting location accounts for more phenotypic variation in ginseng than planting condition (wild vs. cultivated), genetic distance, and geographic distance combined, suggesting that phenotypic plasticity in microenvironments plays a large role in building ginseng vegetative phenotypes. In chapter 3, I examine the potential role of human planting in shaping ginseng genetic and phenotypic variation though conducting and analyzing key informant interviews using the interpretive framework of ethnobotany: the study of people and their relationships with plants. I analyze interviews with 34 growers representing 30 independently owned ginseng planting operations (15 forest farm and 15 artificial shade), many of whom also contributed genetic samples to my chapter 2 study. I find that striking imbalances in access to local seed sources drive human-assisted gene flow from artificial shade gardens in Wisconsin and Ontario to Appalachian forests via seed trade with forest farmers. I also find preliminary evidence of ginseng phenotypes that may be experiencing unconscious selection, including early growth and phenology in seeds originating from Wisconsin. Future common garden experiments should verify and test the stability of these traits across different growing environments and developmental stages. In chapter 4, I employ an evolutionary lens to examine the potential impact of wild harvesting on ginseng phenotypes using digital morphometric methods that can control for common sources of museum collections bias. Leveraging publicly available digital herbaria collections through the Mid Atlantic Herbaria Consortium, I collected and analyzed phenotypic data on N=1,000 individuals to examine temporal and geographic phenotypic variation in ginseng herbarium specimens from museum collections representing over 195 years and 31 U.S. states and Canadian provinces. I find that ginseng plants in the sample herbaria population showed declining leaflet areas, leaflet circularity, and peduncle-petiole ratios and increasing proportions of marginal teeth over time—differences that were especially pronounced before and after 1920. While my results lend support to previously published hypotheses of human-induced dwarfing, my results also highlight the potential role of other factors influencing phenotypic trends in ginseng herbaria, including unconscious selection from widespread introduction of artificial shade ginseng seed and collections bias. In this dissertation, I explore the potential human influences of genetic and phenotypic variation in an economically and culturally significant medicinal plant species. The results of this work identify native wild lineages to prioritize for germplasm conservation and can inform seed banking and trade partnerships among artificial shade and forest farm growers. In addition, my work contextualizes human influence on medicinal plant evolution within the anthropological domestication literature and establishes an analytical framework for future comparative evolutionary work on medicinal plants and domesticated food crops. In doing so, this work contributes to a developing evolutionary anthropology research programs that support conservation and broader societal impact goals within local ecosystems.