Pennsylvania Smartweed (Persicaria pensylvanica) Has Tiny Pink Flowers

Summary: Pennsylvania Smartweed (Persicaria pensylvanica), an annual New World wildflower, has tiny pink flowers.

Pennsylvania smartweed (Polygonum pensylvanicum), James Woodworth Prairie Preserve, Glenview, Cook County, northeastern Illinois: Frank Mayfield (gmayfield10), CC BY SA 2.0, via Flickr

Pennsylvania smartweed (Persicaria pensylvanica) is a New World annual wildflower that has tiny pink flowers and a lengthy blooming period from May through October.

Persicaria pensylvanica thrives in disturbed, moist, open landscapes. Preferred habitats include marshes, meadows, roadside ditches, streamsides, swamps and wetland margins. The plucky wildflower easily tolerates gravel, mudflats, rocks and sand.

The New World native accepts a range of sunlight requirements. Open habitats offer full sun, but the unfussy wildflower tolerates dappled sunlight and partial shade.

Common names for Persicaria pensylvanica are Pennsylvania smartweed, pink knotweed and pinkweed.

The annual’s fibrous root system centers on a shallow taproot. The straight, tapering, vertical primary root grows downward. Subsidiary rootlets sprout laterally.

Stems range in height from 2 to over 4 feet (0.6 to 1.21 meters). Stem height may even measure 6 feet (1.82 meters).

Lance-shaped leaves form alternate arrangements along stems. Green leaves, which sometimes display brownish purple splotches, contrast well with reddish-tinged stems. Pinkweed’s leaf blade has entire edges, that is, smooth, untoothed margins.

A ribbed sheath, known as an ocrea (Latin: ocrea, “legging”), surrounds nodes, the points of attachment for flowers and leaves. Green sheaths have purplish or reddish brown tinges.

The profuse blooming of tiny pink flowers may occur over a lengthy period, from as early as May to as late as October. Small, five-parted, whitish pink flowers are borne on dense racemes (Latin: racemus, “cluster of grapes”). Clusters occur as axillary (at leaf-stem junction) and terminal (at stem top) growths.

Pink knotweed’s seeds are black and shiny, with a flattened, roundish shape. Seeds are popular food sources for such waterfowl as ducks and geese. Mourning doves (Zenaida macroura), Northern bobwhites (Colinus virginianus) and ring-necked pheasants (Phasianus colchicus) join waterfowl in appreciation of pink knotweed seeds. Small mammals that consume the seeds include fox squirrels (Sciurus niger), muskrats (Ondatra zibethicus) and white-footed mice (Peromyscus leucopus).

The pink-flowered New World native claims homelands in Canada and the United States. Pennsylvania smartweed occurs natively in Canada from the easternmost prairie province of Manitoba eastward through Ontario, Quebec, New Brunswick and Nova Scotia.

For the island of Newfoundland, Pennsylvania smartweed is considered as an introduced species by Canadensys, an online biodiversity database maintained by members of the Canadian Biodiversity Information Facility (CBIF) and the Global Biodiversity Information Facility (GBIF). The U.S. Department of Agriculture’s PLANTS Database considers it as native to the large Atlantic Ocean island.

Pennsylvania smartwood is not found in any of Canada’s three territories. Nor does its native range include three western provinces, from British Columbia westward through Saskatchewan. The annual wildflower is not native to Labrador or Prince Edward Island.

In the United States, Pennsylvania smartweed occurs natively in Alaska and in all but three of the Lower 48 states. Stateside, the long-blooming wildflower is not native to Idaho, Utah or Washington. Nor does it occur natively in Hawaii, Puerto Rico or the U.S. Virgin Islands.

Pennsylvania smartweed is a member of the Polygonaceae, known commonly as buckwheat, knotweed or smartweed family. The name of Polygonaceae acknowledges the swollen nodes, or points where new growth appears along stems, that characterize the family’s type genus, Polygonum (Ancient Greek: πολύς, polús, “many” + γόνυ, gónu, “joint, knee”). A sheath of stipules (Latin: stipula, “stalk, straw”), small leaflike outgrowths at the base where petioles, or leafstalks, emerge along stems gives the nodes a swollen appearance.

Taxonomic pioneer Carl Linnaeus (May 23, 1701-Jan. 10, 1778) named and classified Pennsylvania smartweed’s original genus, Polygonum. In 2005, the Flora of North America (FNA) Ed Committee designated Persicaria pensylvanica as the pink-flowered wildflower’s accepted name and Polygonum pensylvanicum as an accepted synonym. The genus name of Persicaria reflects the similarity of species’ leaves to those of peach trees (Latin: persicum, “peach, Persian fruit”).

The pretty pink pastels of Pennsylvania smartweed’s flowers draw attention in natural landscapes. The pink wildflower’s lengthy blooming period qualifies Pennsylvania smartweed for showy placements in native plant gardens. The profusion of tiny pink flowers, especially as terminal clusters, also shows well in roadside ditches about one mile northeast of my home.

Pennsylvania smartweed (Polygonum pensylvanicum), Huffman Prairie, Dayton, southwestern Ohio: Andrew C (acryptozoo), CC BY 2.0, via Flickr

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Pennsylvania smartweed (Polygonum pensylvanicum), James Woodworth Prairie Preserve, Glenview, Cook County, northeastern Illinois: Frank Mayfield (gmayfield10), CC BY SA 2.0, via Flickr @ https://www.flickr.com/photos/gmayfield10/4538346916/

Pennsylvania smartweed (Polygonum pensylvanicum), Huffman Prairie, Dayton, southwestern Ohio: Andrew C (acryptozoo), CC BY 2.0, via Flickr @ https://www.flickr.com/photos/acryptozoo/21143913879/

For further information:

Abbey, Timothy. “Weed of the Month: Pennsylvania Smartweed.” PennState Extension > Plants and Pests > Green Industry > News > 2015. March 4, 2015.
Available @ http://extension.psu.edu/plants/green-industry/news/2015/pennsylvania-smartweed

“Common Name Arrow-Leaved Tearthumb (Arrowleaf Tearthumb).” Friends of the Wild Flower Garden > Archive > Plants - Common Name List.
Available @ http://www.friendsofthewildflowergarden.org/pages/plants/arrowleaftearthumb.html

Davis, Lee; USDA NRCS Northeast Plant Materials Program. USDA NRCS (Natural Resources Conservation Service) PLANTS Database > Plant Fact Sheet. Last edited June 8, 2009.
Available @ http://plants.usda.gov/factsheet/pdf/fs_pope2.pdf

“Pennsylvania Smartweed Persicaria pensylvanica laevigata.” Illinois Wildflowers > Prairie Wildflowers.
Available @ http://www.illinoiswildflowers.info/prairie/plantx/pa_smartweedx.htm

“Persicaria pensylvanica (L.) G. Maza.” Go Botany > Simple Key > All Other Flowering Non-Woody Plants > All Other Herbaceous Flowering Dicots.
Available @ https://gobotany.newenglandwild.org/species/persicaria/pensylvanica/

“Persicaria pensylvanica (L.) M. Gomez.” Digital Atlas of the Virginia Flora.
Available @ http://vaplantatlas.org/index.php?do=plant&plant=3230

“Persicaria pensylvanica (Linnaeus).” eFloras > Flora of North America > Flora Taxon.
Available @ http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=250037745

“Persicaria pensylvanica (Linnaeus) M. Gómez de la Maza.” Canadensys > VASCAN (Vascular Plants of Canada Database).
Available @ http://data.canadensys.net/vascan/taxon/8153?lang=en

Stanford, E.E. “Polygonum pensylvanicum and Related Species.” Rhodora, vol. 27, no. 322 (October 1925): 173-184.
Available via Biodiversity Heritage Library @ http://www.biodiversitylibrary.org/page/587786

Tenaglia, Dan. “Polygonum pensylvanicum L.” Missouri Plants > Pink Flowers, Leaves Alternate.
Available @ http://www.missouriplants.com/Pinkalt/Polygonum_pensylvanicum_page.html