Purple Loosestrife

2016 October 8

While biking to work on July 27, 2016, I spotted these vibrantly purple flowers growing beside the ditch alongside the road:


While it is a rather pretty flower, I would like to call your attention to one alarming fact: It is growing in immediate competition with Tansy, one of our most aggressively invasive species. And it is thriving.


It is also not something that I’ve seed in the area previously, suggesting very strongly that it, too, is an invasive. And in fact, it is the notorious Purple Loostrife, Lythrum salicaria. These are wetland plants that, as you might guess from the number of blossoms, are very prolific seed producers. Here is a closeup of one of the blossoms:


One odd thing is that there appear to be two different types of anther (the pollen-producing parts) in the blossom. It looks like there are green-and-white anthers projecting out of the center of the blossom, and then there are pale yellow ones in the blossom interior. I don’t know if the anthers change color as they grow out, or if the yellow ones and the green ones are actually fundamentally different structures.

Blooming goes on for quite a long time. The flower spike projects up with fresh buds at the top even while the flowers are blooming vigorously at the bottom. The webbing on this stalk is probably tiny little spiders.


So, purple loosestrife is mainly known for getting established in wetland areas, and then crowding out the plants that were already there, like cattails. This dramatically changes the whole ecology of the wetland, since the animals that eat and shelter under cattails can’t make do with the loosetrife. And, the loosestrife produces millions of tiny little seeds that spread around easily and remain viable in the soil for years, so once it gets going it is pretty hard to eradicate. Now that it is in the area, I guess we are likely to see how it will affect our local wetlands pretty quickly.

Although, there are a number of insects that have been found to be effective in knocking back the purple loosestrife stands, in particular two species of leaf beetles and three species of weevils. Four of these beetle species have been released in Minnesota since 1992, and are probably moving into the area hot on the heels of the plants themselves.

Maybe I’ll be posting pictures of some of those beetles one of these days.

An update (August 3, 2021): It has now been 5 years since I took these pictures, and the patch that I photographed then is still the only one along that whole stretch of road. There are maybe twice as many plants in the patch, but it hasn’t really spread or colonized new areas. I suspect that the loosestrife-eating insects have caught up to them, and really put a crimp in their invasive properties, at least locally. That’s pretty encouraging.

2 Responses
  1. Carole permalink
    October 8, 2016


  2. Mark Sturtevant permalink
    October 14, 2016

    This stuff is everywhere. Bees love ’em, and that is a plus, but yes it does outcompete native plants.

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