Ontario Weeds: Pennsylvania smartweed

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Excerpt from Publication 505, Ontario Weeds, Order this publication

Table of Contents

  1. Name
  2. Other Names
  3. Family
  4. General Description
  5. Leaves
  6. Flowers and Fruit
  7. Habitat
  8. Similar Species
  9. Related Links

Name: Pennsylvania smartweed, Polygonum pensylvanicum L.,

Other Names: renouée de Pennsylvanie, Pinkweed, persicaire glanduleuse

Family: Buckwheat or Smartweed Family (Polygonaceae)

General Description: Native to North America and very similar to Pale smartweed in general shape and habit of growth.

Photos and Pictures

Pennsylvania smartweed.

Lady's Thumb. A. Plant. B. Portion of stem with leafstalk and ocrea. Pale smartweed. C. Portion of stem with lower surface of leaf blade, leafstalk and ocrea. Pennsylvania smartweed. D. Portion of lower stem with leafstalk and ocrea. E. Portion of upper stem with leaf stalk and ocrea showing stalked glands.
Lady's Thumb.
A. Plant. B. Portion of stem with leafstalk and ocrea. Pale smartweed. C. Portion of stem with lower surface of leaf blade, leafstalk and ocrea. Pennsylvania smartweed. D. Portion of lower stem with leafstalk and ocrea. E. Portion of upper stem with leaf stalk and ocrea showing stalked glands.

Leaves: Distinguished from Pale smartweed by the absence of matted whitish hair on the undersurface of lower leaves although a few, scattered, short, straight hairs may be present; by the absence of, or only occasional presence of tiny yellowish, unstalked glands on the undersurfaces of upper leaves; by the presence of orange to red or purplish, distinctly stalked glands (glandular hairs) on the upper stems below and in the flower spikes.

Flowers & Fruit: Distinguished from Pale smartweed by the deep pink to reddish colour of the flowering spikes; and by the larger "seeds" that are round-ovate, flattened, slightly hollowed on one side but not the other, and about 3mm (1/8in.) long by 2.5mm (1/10in.) wide; their larger size giving the spikes a coarser texture than in Pale smartweed. Flowers from July to September.

Habitat: Pennsylvania smartweed is native to moist soils in much of southern Ontario. It occurs as a weed in meadows, hay fields, depressional areas in cultivated land, and in roadside ditches.

Similar Species: It is distinguished from lady's-thumb by the complete absence of hair from the surface of the ocrea, the complete absence of a fringe of hair from the margin of the ocrea, the presence of stalked glands on the upper stems, and by its coarser spikes and larger seeds.

Related Links

... on general Weed topics
... on weed identification, order OMAFRA Publication 505: Ontario Weeds
... on weed control, order OMAFRA Publication 75: Guide To Weed Control

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