Polygonum aviculare L.
Common Name: KNOTWEED
Coefficient of Conservatism: *
Coefficient of Wetness: 3
Wetness Index: FACU
Physiognomy: Ad A-Forb

A common weed of both Old and New Worlds, known in Michigan since the First Survey (1838), and in part native. Its low stature permits it to endure mowing, and it survives in highly calcareous as well as saline areas. Sometimes on sandy shores or rock outcrops, but usually a durable and obvious weed of cleared and disturbed sites such as roadsides, lawns and gardens, sidewalk cracks, and railroad banks.

Costea, Tardif, & Hinds (2005) recognize six subspecies, of which several are common in Michigan. “Heterophyllous” plants with much-reduced leaves on flowering branches and sometimes ± erect habit are typical hexaploid subsp. aviculare, relatively frequent and introduced from Eurasia. Plants with the leaves more uniform or only gradually changing in size are subsp. depressum (Meisner) Arcangeli, frequently distinguished as P. arenastrum Boreau, a tetraploid, and a very common, much branched and mat-forming element introduced from Europe. A few specimens are the more narrow-leaved subsp. neglectum (Besser) Arcangeli, again introduced from Europe. Plants with boat-shaped tepals and obtuse leaves are subsp. buxiforme (Small) Costea & Tardif (P. buxiforme Small), an entity thought to be native, and the subspecies to which the 1838 First Survey collection belongs.


Alcona County
Alger County
Allegan County
Alpena County
Antrim County
Arenac County
Baraga County
Bay County
Benzie County
Berrien County
Branch County
Calhoun County
Cass County
Charlevoix County
    Including Beaver Island
Cheboygan County
Chippewa County
    Including Drummond Island
Clinton County
Crawford County
Delta County
Dickinson County
Eaton County
Emmet County
Gogebic County
Grand Traverse County
Gratiot County
Hillsdale County
Houghton County
Ingham County
Ionia County
Iron County
Isabella County
Jackson County
Kalamazoo County
Kalkaska County
Kent County
Keweenaw County
    Including Isle Royale
Lake County
Lapeer County
Leelanau County
    Including Fox Islands
    Including Manitou Islands
Lenawee County
Livingston County
Luce County
Mackinac County
Macomb County
Marquette County
Mason County
Mecosta County
Menominee County
Midland County
Monroe County
Montmorency County
Muskegon County
Newaygo County
Oakland County
Oceana County
Ontonagon County
Oscoda County
Ottawa County
Presque Isle County
Schoolcraft County
Shiawassee County
St. Clair County
St. Joseph County
Tuscola County
Van Buren County
Washtenaw County
Wayne County


MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. November 29, 2022. https://michiganflora.net/species.aspx?id=2295.