Invasive Plants of Wisconsin
Purple loosestrife is an invasive species of sunny wetlands. As illustrated above, it can be very aggressive and it displaces native species. Once established the plants can persist for many years, eventually producing large clumps and producing numerous seeds to spread to other sites.
The bright rose-purple flowers are very conspicuous and are usually present from late June into fall in northern Wisconsin. Leaves are simple, entire (no teeth on the margin), and sessile (attached directly to the stem without a petiole).