Purple Loosestrife (Lythrum salicaria)
Purple loosestrife (Lythrum salicaria) is an invasive perennial plant that is spreading rapidly in North American wetlands, shorelines, and roadside ditches. Thick stands of purple loosestrife crowd out native plants and reduce food, shelter, and nesting sites for wildlife, birds, turtles, and frogs. After multiple introductions in the 1800s for bee keeping, as an ornamental plant, and in discarded soil used as ballast on ships, this European species has invaded nearly every U.S. state and at least six Canadian provinces.
Gardeners, waterfowl hunters, and other outdoor enthusiasts should know how to identify purple loosestrife — detecting new infestations can prevent the spread of this plant. Report new sightings and help control purple loosestrife.
Identify Purple Loosestrife
- Mature plants have many stems that grow from a root crown (2)
- Root crown
- Dead stems stand until spring
- Height 3 to 7 feet (1 to 2 meters)
- Spike covered with many flowers
- Downy, smooth-edged leaves
- Leaves usually paired, opposite
- Stem has ridges
- Flower has several pink-purple petals
What You Can Do
- Learn to recognize purple loosestrife.
Follow Minnesota Aquatic Invasive Species Laws:
- Clean all aquatic plants, animals and mud from watercraft, trailers, docks, lifts, anchors and other recreational equipment before leaving access.
- Drain water-related equipment (boat, ballast tanks, portable bait containers, motor) and drain bilge, livewell and baitwell by removing drain plugs before leaving water access. Keep drain plugs out while transporting watercraft.
- Dispose of unwanted bait, worms and fish parts in the trash.
- Scrub soles of footwear with stiff-bristled brush.
- Spray watercraft and equipment with high-pressure water, or
- Rinse with very hot water, or
- Dry for at least 5 days.
Report New Sightings (less than 100 plants) — note exact location; wrap a plant fragment of stem, leaves and flower spike in a wet paper towel, place in a sealed plastic bag; and call a Minnesota DNR Invasive Species Specialist (see www.mndnr.gov/invasives/contacts.html), 1-888-MINNDNR or (651) 259-5100; or the Minnesota Sea Grant Program in Duluth, (218) 726-8712.
Know the Rules!
Specimens are needed to confirm sightings, but some jurisdictions prohibit or discourage possession and transport of purple loosestrife and other invasive aquatic plants and animals. Contact your local natural resource management agency for instructions. Unauthorized introduction of plants or fish into the wild is illegal. Protect your property and our waters.
- Species Profile: Purple Loosestrife
- Purple Loosestrife: What You Should Know, What You Can Do
- Biological Control of Purple Loosestrife, 4-H Leader's Manual
- Where Have All the Purple Flowers Gone? (Seiche, Sept. 2002)
- Preparing for Purple Eaters (Seiche, August 2001)
- Seeing Purple? Is It Loosestrife? (Seiche, Sept. 2000)
- Publication: Purple Loosestrife WATCH Card
- Publication: Aquatic Invasive Species WATCH Cards (Full Deck)