Equisetum fluviatile (Water Horsetail)
|Also known as:|
|Habitat:||part shade, sun; bogs, swamps, lakes, streams, ditches; standing water up to 3 feet deep|
|Fruiting season:||late spring, summer|
|Plant height:||2 to 4 feet|
|Wetland Indicator Status:||GP: OBL MW: OBL NCNE: OBL|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Leaves and stems:
The sterile stem is green and usually has whorled branches that are spreading to ascending. The “leaves” are reduced to a sheath that surrounds the stem, with 12 to 24 narrow, black-brown teeth around the top that occasionally have a narrow band of white around the edge.
Water Horsetail can create very large, dense colonies, often in the quiet waters of lakes and ditches. There are 2 other Equisetum species that have spreading to ascending branches: Field Horsetail (Equisetum arvense) and Marsh Horsetail (E. palustre). Of these, only E. fluviatile has a stem with a large central cavity so it compresses easily when squeezed. When branches are absent, E. fluviatile resembles Tall Scouring Rush (E. hyemale) or Smooth Scouring Rush (E. laevigatum), both of which have sheath teeth that usually drop off and do not persist. E. fluviatile hybridizes with E. arvense and their offspring, Equisetum × litorale, may be expected where the parents are both present. The hybrid closely resembles E. palustre but the first branch internode is longer than the associated stem sheath, where on E. palustre it is shorter. When trying to determine if the first branch internode is longer or shorter than the stem sheath, it is important to look at the lowest branch on the stem as those higher up the stem may have different lengths.
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- stem sheath, without branches
- emerging Water Horsetail in shallow water
- old stems from the previous year with new stems for the current year
- a colony of Water Horsetail
- a colony of Water Horsetail, most without branches
- Water Horsetail in a bog
Photos by K. Chayka taken in Itasca and Ramsey counties. Photos courtesy Cindy Hoffmann taken at Edenbrook Conservation Area, Hennepin County. Other photos courtesy Peter M. Dziuk.
Have you seen this plant in Minnesota, or have any other comments about it?