Erect Knotweed

(Polygonum erectum)

Erect knotweed is a small, unassuming herbaceous plant with oval-shaped leaves and multiple branches. It has tiny white flowers. As its name suggests, this species of knotweed grows upright unlike some of its sprawling relatives. Erect knotweed is interesting because it produces two different forms of fruit or achene in proportions that depend on the time of year (seasonally controlled achene dimorphism). The two types are smooth (which are elongated) and tubercled (which are more round shaped and textured). Smooth erect knotweed achene are only produced by the plant late in its growing season and germinate quickly. Tubercled achenes are produced during the summer and into the fall but are more unreliable as to how quickly they will germinate. The tubercle achenes wait until the environmental conditions are just perfect before germinating, and it may be over a year before the seeds sprout.

Erect knotweed seeds have been found in archeological contexts in Arkansas as well as Tennessee, Kentucky, Missouri, and Illinois beginning around 1000 BC and continuing into the Mississippi period. Evidence of domestication of erect knotweed first dates to around 1AD in Kentucky (Muller 2018). Erect knotweed seed assemblages that are largely made up of smooth achene indicates that human intervention has altered the plant’s natural achene dimorphism to make planting more reliable and controllable by people. When you plant a seed, you want it to germinate reliably (like the smooth achene do), not wait for an unknown amount of time before germinating (as would be the case for the tubercled achene).

Erect Knotweed References

Mueller, Natalie G.

2017a   An Extinct Domesticated Subspecies of Erect Knotweed in Eastern North America: Polygonum erectum subsp.watsoniae (Polygonaceae). A Journal for Botanical Nomenclature 25(2):166-179.

2017b    Evolutionary “Bet-Hedgers” under Cultivation:  Investigating the Domestication of Erect Knotweed (Polygonum erectum L.) using Growth Experiments.

2017c    Seeds as Artifacts of Community of Practice: The Domestication of Erect Knotweed in Eastern North America. Ph.D. Dissertation. Washington University in St. Louis.

2018   The earliest occurance of a newly described domesticate in Eastern North America: Adena/Hopewell communities and agricultural innovation. Journal of Anthropological Archaeology 49:39-50.

 2019   Documenting the Evolution Agrobiodiversity in the Archaeological Record: Landraces of a Newly Described Domesticate (Polygonum erectum) in North America. Journal of Archaeological Method and Theory 26:313-343.