Sagittaria rigida (Sessile-fruited Arrowhead)
|Also known as:|
|Family:||Alismataceae (Water Plantain)|
|Habitat:||part shade, sun; sandy or muddy soil; lake and pond edges, swamps, swales|
|Bloom season:||July - September|
|Plant height:||6 to 30 inches|
|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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Flowers are whorled in groups of 3 in a spike-like raceme at the top of a naked stem. There are usually both male and female flowers on the same stem, but sometimes a stem is all female. Both genders are about 1 inch across with 3 broad white petals and 3 small pale green sepals behind the flower. Female flowers are stalkless or nearly so, and have a bulbous green center, covered in tiny carpels.
Behind the flower are 3 small pale green to brownish sepals. At the base of the whorl are 3 broadly triangular to egg-shaped bracts, less than ¼ inch long. The bracts shrivel up quickly, the brown, papery remains persisting through fruiting. A plant has 1 or more flowering stems, each with 2 to 8 whorls of flowers.
Leaves and stems:
A rosette of toothless, hairless basal leaves surrounds the flowering stems. Emersed leaves are typically narrowly lance-elliptic, the blade up to 6 inches long, on 3-sided stalks up to 20 inches long.
Submersed leaves are more grass-like, lance-linear, tapering to a sharp point at the tip. Flowering stems are weak and often bent near the lowest whorl of flowers. This species has stolons (horizontal stems) but not rhizomes.
Of the 6 Sagittaria species in Minnesota, Sessile-fruited Arrowhead is most easily distinguished by (you guessed it) its stalkless female flowers and fruits. The leaves are similar to Crested Arrowhead (Sagittaria cristata) and Grass-leaved Arrowhead (S. graminea), both of which have long, slender stalks on all its flowers and fruits. The broader leaves of Sessile-fruited Arrowhead may resemble those of a Water Plantain (Alisma species) but their flowers are in branching clusters and are only about ¼ inch across.
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- Sessile-fruited Arrowhead plants
- Sessile-fruited Arrowhead along a lake shore
- Sessile-fruited Arrowhead in deeper water
Photos by K. Chayka taken in Pine and Washington counties. Photos courtesy Peter M. Dziuk taken in Kanabec, Pine and Washington counties.
Have you seen this plant in Minnesota, or have any other comments about it?