Erect Knotweed

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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 Number Major Reference Family Genus and Species Iowa Culture
13AM403 Powell, 2005 POLYGONACEAE Polygonum erectum O
13BV1 Asch and Green, 1992 POLYGONACEAE Polygonum cf. erectum MC
13CK15 Asch and Green, 1992 POLYGONACEAE Polygonum erectum MC
13DA110 Lensink et. al, 1995 POLYGONACEAE Polygonum erectum GO
13DA264 Asch, 1996 POLYGONACEAE Polygonum erectum GO
13DB497 Powell, 2002 POLYGONACEAE Polygonum erectum TLW
13DM140 Hollinger, 1999 POLYGONACEAE Polygonum erectum O
13LA1 Hollinger, 2005; Hollinger, 1999 POLYGONACEAE Polygonum erectum O
13LA12 Dunne, 2002 POLYGONACEAE Polygonum cf. erectum MW/ELW
13LA38 Asch and Green, 1992 POLYGONACEAE Polygonum erectum MW/ELW
13LA309 Powell and Lopinot, 2000 POLYGONACEAE Polygonum erectum LLW
13LE110 Hollinger, 2005; Zalucha, 1999 POLYGONACEAE Polygonum erectum MLW/O
13LE117B Zalucha, 1999 POLYGONACEAE Polygonum erectum ELW
13MA208 Asch and Green, 1992 POLYGONACEAE Polygonum erectum O
13MA209 Asch and Green, 1992 POLYGONACEAE Polygonum erectum O
13ML361 Green and Billeck, 1993 POLYGONACEAE Polygonum sp. G
13OB4 Asch and Green, 1992 POLYGONACEAE Polygonum cf. erectum MC
13WD88 Dunne, 2005 POLYGONACEAE Polygonum cf. erectum GO

 

Key
MW Middle Woodland
ELW Early Late Woodland
MLW Middle Late Woodland
LLW Late Late Woodland
TLW Terminal Late Woodland
GO Great Oasis
MC Mill Creek
G Glenwood
O Oneota

Two photographs of knotweed plants

Two photographs of knotweed plants

 

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