Purple loosestrife is a perrenial herb that prefers to grow in moist soil such as in marshes, river and stream banks, pond edges, reservoirs, and in ditches. It has lance-shaped leaves and a woody stem. It produces magenta flower spikes in the summer and can grow from four to ten feet tall. Each plant may produce two to three million, minute seeds per year and also reproduces vegetatively. ””Guaranteed sterile” cultivars of purple loosestrife are actually highly fertile and able to cross freely with purple loosestrife and with other native Lythrum species. Therefore, outside of its native range, purple loosestrife of any form should be avoided.”

Originally from Europe purple loosestrife was introduced to the northeastern U.S. and Canada in the 1800s, for ornamental and medicinal uses. It is still widely sold as an ornamental. Purple loosestrife now occurs in every state except Florida and all Canadian provinces.

Purple loosestrife outcompetes native plants and forms dense, homogeneous stands that are not as nutritious for animals, alteration of the wetlands and reduce habitat for waterfowl.

Small purple loosestrife plants can be pulled before they go to seed. Larger plants should be treated with herbicide. The Galerucella beetle (Galerucella calmariensis) is being used in some areas as biocontrol for purple loosestrife. The beetle is from the native range of purple loosestrife.

Alternative plants that may be planted in place of purple loosestrife are native species of Liatris (blazing star) which are an important source of nectar many native species of butterflies and other insects.

(From: http://www.nps.gov/plants/ALIEN/fact/lysa1.htm and http://www.invasiveplants.net/Insects/galerucella.htm)