Erect Knotweed


Table of Contents

Erect knotweed (Polygonum erectum L.)

Erect knotweed was cultivated in ancient Iowa and may have been domesticated. It flowers and fruits throughout the summer and into the fall until a killing frost. A synchronized flowering period late in the growing season results in simultaneous ripening of a quantity of small-sized starchy seeds during October. Erect knotweed can be harvested by pulling up the plants by the roots and shaking or stripping off the fruits. Today it grows in abundance in cattle and hog pastures and feedlots, and along dirt and gravel roads in flood plains.

Archaeologists report discoveries of cultivated erect knotweed in Iowa beginning as early as the Middle Woodland, 2,000 years ago, although it is more common in Late Woodland, Great Oasis, Mill Creek, and Oneota contexts. Like goosefoot, its starchy seed could be cooked in a variety of ways. Among historic Native Americans, it also had medicinal purposes, and varieties of knotweed were used in dyes and for smoking.

Although knotweed is frequently reported at Iowa sites, taxonomic difficulties and problems in identifying species exist. Only instances where researchers identified seeds to genus and species, or indicated the likelihood that the archaeological specimens represented cultivated forms, are listed on the table and at the site locations shown on the map.

Major References

Asch, David and William Green 1992
Green, William and Shelly Gradwell 1995

Map of Iowa with hot pink dots that indicate prehistoric sites known to have cultivated knotweed
Iowa Sites
Site NumberMajor ReferenceFamilyGenus and SpeciesIowa Culture
13AM403Powell, 2005POLYGONACEAEPolygonum erectumO
13BV1Asch and Green, 1992POLYGONACEAEPolygonum cf. erectumMC
13CK15Asch and Green, 1992POLYGONACEAEPolygonum erectumMC
13DA110Lensink et. al, 1995POLYGONACEAEPolygonum erectumGO
13DA264Asch, 1996POLYGONACEAEPolygonum erectumGO
13DB497Powell, 2002POLYGONACEAEPolygonum erectumTLW
13DM140Hollinger, 1999POLYGONACEAEPolygonum erectumO
13LA1Hollinger, 2005; Hollinger, 1999POLYGONACEAEPolygonum erectumO
13LA12Dunne, 2002POLYGONACEAEPolygonum cf. erectumMW/ELW
13LA38Asch and Green, 1992POLYGONACEAEPolygonum erectumMW/ELW
13LA309Powell and Lopinot, 2000POLYGONACEAEPolygonum erectumLLW
13LE110Hollinger, 2005; Zalucha, 1999POLYGONACEAEPolygonum erectumMLW/O
13LE117BZalucha, 1999POLYGONACEAEPolygonum erectumELW
13MA208Asch and Green, 1992POLYGONACEAEPolygonum erectumO
13MA209Asch and Green, 1992POLYGONACEAEPolygonum erectumO
13ML361Green and Billeck, 1993POLYGONACEAEPolygonum sp.G
13OB4Asch and Green, 1992POLYGONACEAEPolygonum cf. erectumMC
13WD88Dunne, 2005POLYGONACEAEPolygonum cf. erectumGO


MWMiddle Woodland
ELWEarly Late Woodland
MLWMiddle Late Woodland
LLWLate Late Woodland
TLWTerminal Late Woodland
GOGreat Oasis
MCMill Creek

Two photographs of knotweed plants

Two photographs of knotweed plants


Image Credit:
Wendy and Michael Scullin
Melanie Riley and Mary Kathryn Rocheford, OSA (map)