Decodon verticillatus (Swamp Loosestrife)

Plant Info
Also known as: Water Willow
Genus:Decodon
Family:Lythraceae (Loosestrife)
Life cycle:perennial
Origin:native
Status:
  • State Special Concern
Habitat:part shade, sun; swamps, lake shores, shallow mucky water
Bloom season:July - September
Plant height:2 to 4 feet
Wetland Indicator Status:GP: OBL MW: OBL NCNE: OBL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

Pick an image for a larger view. See the glossary for icon descriptions.

Detailed Information

Flower: Flower shape: 5-petals Cluster type: whorled

[photo of flowers] Pinkish purple flowers whorled in a dense cluster around the stem at the leaf axils. Flowers have 4 to 7 crinkled petals (usually 5), each about ¼ inch long, elliptical but often fleeting and not always easy to distinguish. 8 to 10 white-tipped pink stamens arch out in a spidery array extending nearly double the length of the petals. Over-all flower structure is nearly 1 inch across.The calyx holding the flower is a thin walled, paper-like cup with gnarly appendages. Multiple flowering stems, rarely branched, shoot from the base of the plant.

Leaves and stem: Leaf attachment: opposite Leaf attachment: whorl Leaf type: simple

[photo of leaves] Leaves are opposite or more often in whorls of 3 or 4, elliptical to lance-like, tapered similarly at both ends, 2 to 8 inches long, ½ to 2 inches wide, toothless, finely hairy on the underside and smooth on the upper surface, the mid-vein reddish near base, on a short stalk. Stems are long and arching, up to nearly 10 feet in length but the overall plant height rarely exceeds 3 to 4 feet. Stems root at the tips as they re-meet the substrata, are sometimes slightly hairy, angled with 4 to 6 sides, often pinkish red on blooming canes and woody at the base. 

Fruit: Fruit type: capsule/pod

[photo of fruit] Fruit is a globular capsule up to 1/3 inch across, containing numerous seeds. Capsules persist through winter. Minnesota plants rarely form set seed but spread as clonal mats via re-rooting stems.

Notes:

Being at the northwest fringe of its natural range, Swamp Loosestrife is restricted to lakeshores in east central Minnesota. Because this region has seen such heavy development over the past decades it should come as no surprise that another native species has been put at risk. According to the DNR it has been listed as a Special Concern species since 1984.

Please visit our sponsors

  • Minnesota Native Plant Society

Where to buy native seed and plants ↓

Map of native plant purveyors in the upper midwest

  • Shop for native seeds and plants at PrairieMoon.com!
  • Shooting Star Native Seeds - Native Prairie Grass and Wildflower Seeds
  • Morning Sky Greenery - Native Prairie Plants
  • Minnesota Native Landscapes - Your Ecological Problem Solvers
  • Natural Shore Technologies - Using science to improve land and water

More photos

Photos courtesy Peter M. Dziuk taken at several locations in Anoka county.

Comments

Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Ellen S.
on: 2016-10-29 15:40:39

How can I tell this apart from purple loosestrifge

Posted by: K. Chayka
on: 2016-10-29 16:17:12

Flowers are arranged differently: Decodon verticillatus has flowers whorled in the leaf axils, Lythrum salicaria has a single spike at the tip of a branch.

Posted by: Frances WM - 27170 Lakewood Dr. Isanti MN 55040 (on our property)
on: 2017-09-12 15:38:03

There is a creek that runs through our property called Spirit Creek which runs into the Rum River. The creek is the outlet for Long Lake. This plant is massive, almost to the point of chocking out the creek. Now this year, it has spread onto our shoreline in front of our home on Long Lake. A few years ago I checked with DNR and they said this is the farthest west that they have seen this plant.

Post a comment

Note: All comments are moderated before posting to keep the riff-raff out. An email address is required, but will not be posted—it will only be used for information exchange between the 2 of us (if needed) and will never be given to a 3rd party without your express permission.

For info on subjects other than plant identification (gardening, invasive species control, edible plants, etc.), please check the links and invasive species pages for additional resources.



(required)




Note: Comments or information about plants outside of Minnesota and neighboring states may not be posted because Id like to keep the focus of this web site centered on Minnesota. Thanks for your understanding.