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PURPLE LOOSESTRIFE
Lythrum salicaria

Other Names | Origin & Distribution | Plant Description | Similar Species | Biology | Toxicity | Facts & Folklore

Purple loosestrife in flower; note the many branches. Elongating purple loosestrife stem. Note that the leaves are in pairs, but may also be in whorls of 3. Purple loosestrife seedling with cotyledons and 6 true leaves. Purple loosestrife seedling with cotyledons and 2 true leaves. The stem of purple loosestrife is 4- to 6-sided and may have hairs. Note that the leaves can be in whorls of 3. Purple loosestrife shoots emerging from established roots. Purple loosestrife seeds. Purple loosestrife leaf; note that the leaf attaches directly to the stem. Close-up of purple loosestrife flowers. Purple loosestrife flowering stem.

Family: Loosestrife Family (Lythraceae)

Other Names: blooming sally, bouquet-violet, braune weiderich, flowering sally, foxtail, grass-poly, kill-weed, long-purples, lysimaque rouge, lythrum salicaire, milk willow-weed, partyke, purple lythrum, purple willow herb, purplegrass, rainbow-weed, red sally rosy-strife, rother weiderich, sage-willow, salicaire, spiked loosestrife, spiked soldiers, spiked willow herb, willowweed.

Origin and Distribution: Purple loosestrife is a native of Europe that was likely brought to North America by accident in the early 1800's. It is currently distributed throughout the northeastern part of the United States and adjacent areas in Canada, and it is spreading. In Ohio, purple loosestrife can be found in the north around Lake Erie and in several counties along the Ohio River. It is also prevalent in some northeastern and central parts of the state. Purple loosestrife occurs in natural and disturbed wetland habitats such as marshes, wet meadows, riverbanks, lakeshores, ditches, flooded pastures, and bogs. Although the plant prefers and grows most aggressively in wet areas, it also survives drier conditions.

 

Plant Description: Purple loosestrife is a perennial plant that forms a dense bush consisting of up to 50 stems arising from a shallow root system, which includes a woody crown and rhizomes (horizontal underground stems). Location should be considered when characterizing this plant, as it is a much more aggressive weed when growing in wet areas. It can be identified while in bloom by its purple-magenta flowers that form on distinctive terminal spikes. Also, upper above-ground parts of the plant should appear densely hairy. Purple loosestrife reproduces by seeds and it spreads by rhizomes.

  • Root system - Roots are thick, fleshy and shallow and develop into a large woody crown.
  • Seedlings & Shoots - Young plants look like a small version of the adult.
  • Stems - Stems are upright and grow 2 to 6 feet tall. They are usually branched, have fine hairs, and are either square or 6-sided.
  • Leaves - There are 2 or sometimes 3 leaves at most lower stem nodes. Leaves near the top of the plant are smaller and alternate so there is usually a single leaf at each upper stem node. Leaves attach to stems directly rather than by way of leaf stalks (petioles). Leaves are 1 to 4 inches long, finely hairy, and lance-shaped except for larger leaves that have a heart-shaped base. Leaves turn red before falling off in autumn.
  • Flowers - Many flowers cluster together at the end of slender, upright stems forming long, showy, multi-flowered spikes. Flowers consist of 6 purple-magenta petals that are about 1/4 inch long.
  • Fruits & Seeds - Purple loosestrife forms small seedpods containing many tiny, reddish-brown seeds.
 
Similar Species: Numerous species in the Mint Family (Labiatae) also have opposite leaves and square stems but they usually smell minty. Also, petals of mint flowers are variously fused while purple loosestrife flowers have petals that are separate. Compared with those of mints, purple loosestrife seeds are much smaller and produced in greater numbers. Willowherbs (Epilobium spp.) often resemble young purple loosestrife plants except they are annuals so they do not form the woody root crowns and rhizomes that are characteristics of purple loosestrife.
 

Biology: Purple loosestrife is an attractive plant but it is also an invasive weed in wetlands. Once established, it crowds out other species forming dense monospecific stands that are impenetrable by boat and difficult to walk through. Such dense infestations can also clog irrigation systems. In many states, purple loosestrife has been declared a noxious weed and its sale is prohibited, but it is readily available for purchase in other states. Therefore, it is considered a noxious weed by some people who feel it should be eradicated while others value it as an ornamental, a medicinal plant, or a wildflower and proceed to plant in their gardens. Purple loosestrife begins blooming in July and continues through September. It is not uncommon to find 1 to 2 million seeds produced per plant and seeds can live for several years in the soil seed bank. This buried seed reserve along with its rhizomes enable purple loosestrife to spread rapidly once established. Early detection is essential to slow the spread of this prolific perennial. The most effective management is a combination of several practices in an integrated manner. Such measures may include frequent and continued mowing, hand pulling, cultivating, or herbicide applications. Care should be taken to remove any residue that is created as purple loosestrife stem fragments can root producing new plants. Biological control measures are currently being investigated that could aid in long-term management of this invader of wetland habitats.
 

Toxicity: None known.
 

Facts and Folklore:
  • The name 'Lythrum' is from the Greek 'luthron' meaning blood and may refer to either the color of the plant's flowers or its medicinal use as an astringent to stop the flow of blood.

  • 'Salicaria' means 'willow', and the shape of purple loosestrife leaves is similar to that of willows.

  • The common name for purple loosestrife in French is 'salicaire', which likely gave rise to such common English names as blooming sally, red sally, and flowering sally.

  • Purple loosestrife has been used in treating many ailments including diarrhea, dysentery, fevers, constipation, and cholera.

  • Japanese beetles are fond of purple loosestrife, which may appear to attract these insect pests in a similar manner as many roses.