Littorella americana (American Shoreweed)
|Also known as:
|American Shore Plantain
|part shade, sun; shallow to 3+ feet deep water; soft water lakes, shores
|June - August
|1 to 4 inches
|Wetland Indicator Status:
|GP: none MW: none NCNE: OBL
|MN county distribution (click map to enlarge):
|National distribution (click map to enlarge):
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Separate male and female flowers are on the same plant (monoecious), both about 3 mm (1/8 inch) long, tubular or cup-like with 4 semi-transparent, greenish white lobes surrounded by 4 lance-oblong green sepals with translucent edging. Male flowers are single with 4 long stamens extending out of the tube, on an erect stalk up to about 1½ inches long arising from the plant base. The 1 to 5 female flowers are clustered at the plant base, stalkless or nearly so, and each with a single long, thread-like style.
Leaves and stems:
Leaves are all basal, erect to spreading to arching, linear, 1 to 4 inches long (rarely longer), 1 to 2.2 mm wide, round in cross-section or nearly so, broadest near the middle, gradually tapering from about the midpoint to a blunt or pointed tip, whitish at the base, bright green above, and have a single vein. Plants are commonly completely submersed but in shallower water may be emersed or become stranded on land when water recedes. Plants form colonies from both stolons and rhizomes (above and below ground horizontal stems).
Fruit is a nutlet up to 3 mm (1/8 inch) long containing a single seed; seeds are cylindric, brown or black.
American Shoreweed is an uncommon aquatic primarily found in soft water lakes with sandy or gravelly substrates, in or near the Boundary Waters Canoe Area Wilderness, with scattered populations in north-central Minnesota where it reaches the southwestern tip of its range. Vegetative colonies form in completely submersed populations but it requires emersed plants to bear flowers and fruit. With persistent high water levels over the past several years, we've had some difficulty finding flowering plants, and with our summers becoming wetter in a changing climate that trend is likely to continue. According to the DNR, it is considered rare or vulnerable across much of its US and Canadian range; it is currently a Special Concern species in both Minnesota and Wisconsin.
American Shoreweed is distinguished by its colony-forming habit and basal clumps of linear leaves 1 to 4 inches long and 1 to 2.2 mm wide that have a single vein and are round in cross-section. When flowering, the single male flower is pretty distinctive but the female flowers are much more obscure, hidden in the clump of basal leaves.
Littorella americana, also known by synonym Littorella uniflora or L. uniflora var. americana, is often found with other aquatics that have basal clumps of linear leaves, such as Water Lobelia (Lobelia dortmana), Pipewort (Eriocaulon aquaticum), Quillworts (Isoetes spp.) and others, all of which have flatter leaves rather than round in cross-section.
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- American Shoreweed plant
- a mat of American Shoreweed
- a mat of American Shoreweed
- close-up of male flower
Photos by Peter M. Dziuk taken in Itasca County.
Have you seen this plant in Minnesota, or have any other comments about it?