American Ginseng Biology
American ginseng (Panax quinquefolius L.) is a perennial plant with a unique life cycle. This complexity includes delayed germination (from one and a half up to five and a half years), slow but highly variable maturation to reproductive size, an ability to self or cross-pollinate, and year-to-year aboveground size changes that may show growth or shrinkage. Years of research paint an intricate picture of ginseng's special biology, life cycle, reproduction and habitat.
Species Overview
American ginseng (Panax quinquefolius L.) is an inconspicuous herbaceous plant found in the understory of the Eastern deciduous forest. In fact, to the untrained eye, ginseng looks very similar to many leafy green perennials blanketing the forest floor. These plants experience a sheltered life, literally.
Large trees shade the understory, absorbing sunlight and reducing evaporation from the soil surface. Herbaceous plants, like ginseng, may be particularly sensitive to changes in their stable environment.
Plants adapt their basic body plan in amazing ways in order to fully exploit their environment. Ginseng also has a few evolutionary surprises.
American ginseng, diagram showing how to estimate age by counting bud scars. Credit: E. P. Burkhart, PSU Label by: J. B. McGraw, WVU
Ginseng’s Range in the US and Canada
Map courtesy of the AAFC, Government of Canada
Ginseng’s stem is actually found below ground. During the growing season, this structure, known as a rhizome, develops a bud that will grow into the next year’s visible ginseng plant. Each fall, when the aboveground part of ginseng senesces, a scar is formed on the rhizome. Since one scar is formed per growing season, plants can be aged by counting the scars. Since rhizomes must be left attached to the root, compliance with the 5 year age minimum can be checked when the roots are dug and upon sale.
Rhizomes can also be used (along with seeds) to propagate plants (1) and in fact many old time ginseng harvesters used to plant the rhizomes at harvest to assure continuation of the population. Since the rhizome produces a clone of the parent plant, this mode of reproduction helps to assure propagation of already-successful genotypes. Unfortunately, this mode of propagation is not an option when digging roots for sale, as the rhizome is required to accurately age the plant at the point of sale.
(1) Van der Voort, M. E., B. Bailey, D. E. Samuel, and J. B. McGraw. 2003. Recovery of populations of goldenseal (Hydrastis canadensis L.) and American ginseng (Panax quinquefolius L.) following harvest.
Life History of American Ginseng
Ginseng begins life as a seed, dispersed inside the berry in fall, and remains in the soil through at least two winters (sometimes 3, 4 or 5) prior to germination in spring. The yearly phenology (timing of events within a year) of American ginseng is similar to other summer greens. American ginseng emerges from winter dormancy and begins elongation and leaf expansion in late April or early May, prior to complete closure of the tree canopy. Flowering in reproductive individuals occurs in June and July, followed by fruit production and ripening from July to September and subsequent seed dispersal. Within a year, ginseng plants stay in a particular stage. This does not mean they are passive and unchanging with the passing of seasons, however.
Below are two time lapse sequences captured by J.B. McGraw in 2013 and 2014. Video 1 is a sequence showing a single plant as it emerges in spring. Video 2 shows a mature American ginseng plant as it flowers in summer, then senesces in fall while the environment changes dramatically around it.
Video 1 - To see how a ginseng plant emerges in the spring, watch this time-lapse video of a mature American ginseng as it grows up through the leaf litter on the forest floor.
Video Credit: J.B. McGraw, Spring 2014
Video 2 - For more information on how a ginseng plant grows throughout the year, watch a time-lapse video of a Year in the Life of a Ginseng Plant- 2013. Credit: J.B. McGraw
Ginseng may remain a 1-leaf plant for several years as it accumulates enough stored reserves to grow into a 2-leaf, adolescent ginseng. A 2-leaf ginseng plant may develop flowers and seeds, but reproduction is intermittent and low. Ginseng remains in this 2-leaf stage for another several years before developing into a large adult plant (typically with 3 leaves), which may in old age eventually have 4, or rarely 5 leaves.(1) These large adult plants are the primary targets of harvest. It is important to note that wild American ginseng grows quite slowly compared to plants in cultivation.
Defining these life stages is important for demographic research (the study of changes in population size). Plants at different life stages vary in terms of seed production and mortality. In order to accurately model population growth in American ginseng, life stages that capture these demographic characteristics must be created. This type of classification is referred to as stage-based classification, because the size or stage of the plant, not the age, is used to assign ginseng to groups. Finally, progression of seeds through the seed bank uses age-classification, since seeds do not change in size as long as they remain dormant.
The many year-to-year stages and size transitions of wild American ginseng.
Image credit: wildamericanginseng.org, 2022
It is tempting to describe ginseng embryos (seeds) germinating into a "baby" (new seedling) phase, followed by a "toddler" phase (older 1-leaf plants), then juvenile (2-leaf) plants, which ultimately grow to become mature adults (3-leaf and larger), much like humans. The analogy with human development only goes so far. In fact, unlike humans, ginseng plants can revert to earlier stages, reflecting a ‘plastic’ response to the environment or other adverse conditions. After being browsed by a deer, or experiencing a bad drought, a given plant often comes back the next year reduced in size, lower in reproductive output, and potentially more likely to die.
(1) McGraw, (et al) 2013. Ecology and conservation of ginseng (Panax quinquefolius) in a changing world.
In other words...
Although wild American ginseng plants can increase or decrease in size from one year to the next, when conditions allow, they progress through stages of life a little bit like people do, from helpless small one-leaf 'baby' plants, to two-leaf juveniles that may, in their 'adolescent' phase, produce a seed or two successfully.
Finally, as 'adults', well-established three and four leaf plants can stay around for decades, reproducing occasionally until stress or disease or deer browse or harvest kills them.
Emerging four prong ginseng.
Credit: batcavebotanicals, 2015
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Gallery: Ages & Stages of Wild American Ginseng
(Click to enlarge images.)
Reproduction of American Ginseng
Ginseng does not spread clonally, and therefore populations expand only through production, dispersal and germination of seeds. Ginseng flowers are not showy, but rather small and whitish-green, bunched together in an umbel. Ginseng flowers mature centripetally; flowers on the outside of the umbel blooming before the flowers located in the center of the umbel.
Ginseng has a mixed mating system, meaning that the plant can reproduce via self-fertilization and by outcrossing which refers to an ovum being fertilized by an external pollen source. There are two known pollinators of ginseng: syrphid flies and halictid bees. Both of these insects are generalist pollinators, meaning that they visit multiple species of plants when gathering pollen and nectar.
Pollinators on American ginseng flower.
Gallery Credit: Zachary Bradford
Flower and Berry Development of American ginseng.
Credit: wildamericanginseng.org, 2022
Dispersal of American Ginseng
Ginseng berries are bright red when mature, and contain between one or two (occasionally three) seeds. Ginseng seeds are thought to be dispersed primarily by gravity, but in actuality little is known about ginseng dispersal. Game cameras have been used to see what animals were visiting ginseng plants while seeds were ripe. Check out what we found (image right). Of these animals, which one do you think is the most effective disperser of ginseng seeds?
If you said the bird at the upper left, you would be correct! That is a wood thrush, one of the common birds of the deciduous forest understory whose range corresponds very closely to that of ginseng. Thrushes have been caught on camera near maturing ginseng seeds many times, and in fact some of these times berries were seen in the beak of wood thrushes. Of course, a berry in a beak does not prove thrushes disperse seeds – after all – deer eat ginseng seeds too, but they are destroyed in the gut of a deer. Feeding trials were performed with thrushes using captive birds at the Chattanooga Aquarium in order to determine if seeds are still viable after they're eaten by birds.
(Image right) Wildlife interaction with wild American ginseng, study trail cam footage. Credit: McGraw Labs
The answer is after seeds are ingested, between 5 and 37 minutes, seeds are regurgitated by the birds in good shape, and they are still viable. One of ginseng's seed dispersers was found! This has important implications for migration of ginseng across the landscape. While gravity does little for medium- or long-distance movement of ginseng, birds have the ability to disperse ginseng into new and potentially favorable habitats.
Reference:
Hruska, A. M., Souther, S., and J. B. McGraw. 2014. Songbird Dispersal of American ginseng (Panax quinquefolius).
Swainson's thrush with American ginseng berry, study trail cam footage.
Credit: McGraw Labs