Lythrum alatum
Similar to Lythrum salicaria L.
The native winged loosestrife (Lythrum alatum) most closely resembles purple loosestrife. However, winged loosestrife has alternate leaves, more widely spaced flowers, and is smaller in size (an average of 2 feet or 0.6 m tall) than purple loosestrife.
Other native species that might easily be confused with purple loosestrife on first glance include fireweed (Epilobium angustifolium), blue vervain (Verbena hastata), and blazing star (Liatris spicata), although their preferred habitats are considerably drier.