Weed Seed: Lythrum salicaria (Purple loosestrife)



Common Name

Purple loosestrife


Primary Noxious, Class 2 in the Canadian Weed Seeds Order, 2016 under the Seeds Act.


Canadian: Occurs in all provinces but not in the territories (Brouillet et al. 2016Footnote 1).

Worldwide: Native to northern Africa, Europe and temperate Asia and introduced in North America, Chile, South Africa, Australia and New Zealand (USDA-ARS 2016Footnote 2). It is found throughout the United States except for the extreme southeastern states; abundant in the northeastern region (Kartesz 2011Footnote 3).

Duration of life cycle


Seed or fruit type


Identification features


  • Seed length: 0.5 - 1.0 mm
  • Seed width: 0.3 - 0.5 mm


  • Teardrop or cuneate seed

Surface Texture

  • Seed glistening with fine longitudinal striations


  • Seed dark reddish-brown

Other Features

  • Hilum is a black dot at the wide end of the seed
  • A raphe extends from the hilum to the narrow end of the seed

Habitat and Crop Association

Pastures, meadows, old fields, gardens, wetlands, shores and disturbed areas (Darbyshire 2003Footnote 4). Not usually a weed of agriculture but can grow along field edges near wetlands (CABI 2016Footnote 5).

General Information

Purple loosestrife has been present in North America since the early 19th century, likely transported in ship ballast (Mal et al. 1992Footnote 6). It may also have been planted as a medicinal herb, or brought by beekeepers as a source of nectar (Mal et al. 1992Footnote 6).

It is available from some seed companies as an ornamental (CABI 2016Footnote 5). Disturbed sites with moist soils or seasonally flooded sites are required for establishment (CABI 2016Footnote 5).

Similar species

Hyssop loosestrife (Lythrum hyssopifolia)

  • Seeds of hyssop loosestrife have a similar teardrop shape, prominent raphe and striated surface as purple loosestrife.
  • Hyssop loosestrife seeds (length: 1.0 mm; width: 1.3 mm) are generally larger, a yellowish colour and not elongated as purple loosestrife.


Purple loosestrife (Lythrum salicaria) seeds
Purple loosestrife (Lythrum salicaria) seed, inner side
Purple loosestrife (Lythrum salicaria) capsule and seed

Similar species

Similar species: Hyssop loosestrife (Lythrum hyssopifolia) seeds and capsule
Similar species: Hyssop loosestrife (Lythrum hyssopifolia) seeds
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