Photo credit: © Ellie Buick/Flickr
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Species at a Glance
Purple loosestrife is an upright perennial herb that can grow 0.9-3 m (3-10 ft) high depending on environmental conditions. While gardeners may enjoy the brilliant purple display, its attractiveness doesn’t outweigh the serious threat it poses to ecosystems in the Mid-Atlantic.
Leaves: The body of the leaf is lance-shaped or oblong while the base is usually heart-shaped or rounded. Leaves are stalkless with smooth edges and are sometimes covered in fine, downy hairs. They reach 4-10 cm (1.6-3.9 in) in length and are usually paired and opposite each other down the stem, but can also be whorled in groups of three.
Flowers: Paired or clustered into 10-40 cm (3.9-16 in) long magenta colored spikes. Each flower is complete, containing 5-7 petals that can range in color from pink to purple-red and blooms from June to September.
Fruits/Seeds: Two valve-shaped capsules burst at maturity, releasing seeds in late July or August.
Stems/Roots: Mature plants can have 1-50 square, woody stems arising from a large central taproot. Stems are 4-6 sided, green to purple in color, and are often branching, giving the plant a bushy or woody appearance.
It’s best to identify purple loosestrife during its long period of bloom when the characteristic reddish-purple flower masses can be easily seen. It is often confused with blue vervain (Verbena hastata), which has toothed instead of smooth leaves; blazing star (Liatris spp.), which only has one flowering stalk; and other species of loosestrifes.
Purple loosestrife occurs in freshwater and brackish wetlands, riparian corridors, ditches, and other moist soil areas. It is a successful colonizer and potential invader of any wet, disturbed site in North America.
A long flowering season allows purple loosestrife to produce an estimated two to three million seeds per year from its 30-50 flowering stems. It can also reproduce vegetatively through underground stems at a rate of about 0.3 m (1 ft) per year.
Native to areas of Europe and Asia, purple loosestrife was brought to North America in the early 1800s for ornamental and medicinal uses. It has since spread to almost every state in the U.S. and is widespread in all Mid-Atlantic states.
Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.
Purple loosestrife quickly establishes and spreads, outcompeting and replacing native grasses and other flowering plants that provide high-quality food and habitat sources for wildlife. It forms dense stands that restrict native wetland plants and alter the structural and ecological values of wetlands.
Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).