Ontario Weeds: Swamp 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. Flowers and Fruit
  6. Habitat
  7. Similar Species
  8. Related Links

Name: Swamp smartweed, Polygonum coccineum Muhl.,

Other Names: renouée écarlate, persicaire des marais

Family: Buckwheat Or Smartweed Family (Polygonaceae)

General Description: Perennial, reproducing by seed and by rhizomes that root abundantly from the nodes. Like Water smartweed, Swamp smartweed also occurs in two forms: terrestrial and aquatic. The two smartweeds are very similar and nearly impossible to distinguish from each other before flowering, except that Swamp smartweed never has a leaf-like flange at the top of its ocrea.

Photos and Pictures

Swamp smartweed.

Swamp smartweed.

Swamp smartweed. Underground rhizome with 1 flowering shoot and 1 vegetative shoot.

Swamp smartweed. Underground rhizome with 1 flowering shoot and 1 vegetative shoot.

Flowers & Fruit: The inflorescence is also a spike-like raceme but is usually longer and narrower than that of Water smartweed, the terminal raceme being 2-18cm (4/5-7in.) long and 7-15mm (¼-3/5in.) wide, and less compact than that of Water smartweed; flowers are scarlet to pink or rarely white. Both the terrestrial and aquatic forms have lens-shaped, dark brown to black achenes, 2.3-3mm (1/10-1/8in.) long and wide. Flowers from July to September.

Habitat: Like Water smartweed, Swamp smartweed is also a native plant and occurs in similar habitats throughout Ontario.

Similar Species: It is distinguished from the terrestrial form of Water smartweed by never having a leaf-like flange on its ocrea and from both terrestrial and aquatic forms of Water smartweed by its longer, thinner inflorescence. It is usually coarser than Water smartweed.

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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