Sagittaria rigida (Sessile-fruited Arrowhead)

Plant Info
Also known as:
Genus:Sagittaria
Family:Alismataceae (Water Plantain)
Life cycle:perennial
Origin:native
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):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 3-petals Cluster type: raceme Cluster type: whorled

[photo of female flowers] 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.

[photo of male flowers] Male flowers are on long, slender stalks and have a group of yellow stamens in the center. The stamen stalk (filament) is stout and covered in short yellow hairs.

[photo of bracts and sepals] 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: Leaf attachment: basal Leaf type: simple

[photo of emersed leaves] 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.

[photo of broader leaves] Leaves may be up to 4 inches wide in shallow water or drier conditions, and rarely blades may have narrow lobes at the base.

[photo of submersed leaves] 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.

Fruit: Fruit type: seed without plume

[photo of fruit] Fruit is a globular head of beaked seeds up to ¾ inch in diameter and turns a deep reddish color as seeds ripen. The seed's beak projects at an upward angle with a slight hook at the tip.

Notes:

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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More photos

Photos by K. Chayka taken in Pine and Washington counties. Photos courtesy Peter M. Dziuk taken in Kanabec, Pine and Washington counties.

Comments

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

Posted by: Daniel - Prior Lake
on: 2016-01-04 02:26:13

We are cutting stems in dense patches of narrow leaved cattails and allowing sunlight to other plants. the next year Arrowhead appears.

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