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Sagittaria sagittifolia L.
Common names: arrowhead, giant arrowhead
Fruiting heads with multiple achenes. Achenes winged, obovate to orbicular, beaked, 2.5-5.3 mm long, 1.5-3.5 mm wide, 0.1-0.5 mm thick. Dorsal wing twice as wide as ventral wing, beak apical, erect, 0.3-0.8 mm long. Surface light to dark brown or reddish-brown, rough, sticky, 0-3 resin ducts on each face. Embryo curved-linear, its form visible on surface under testa; endosperm absent.
Helpful distinguishing characters among Sagittaria are relative widths of the wings, presence or absence of wing on faces, and position of beak.
Sagittaria montevidensis Cham. & Schltdl.
Widespread in Europe, temperate, southern and Southeast Asia, Australia, Pacific islands; in the Western hemisphere: Argentina, Cuba, Mexico, Hawaii.
Native in much of Europe, Armenia, Azerbaijan, China, and Russia.
Subarctic to tropical, in quiet, shallow, standing waters, including swamps, reservoirs, rice paddies, river banks, bays.
Sagittaria sagittifolia is a perennial, stoloniferous, aquatic or wetland deep-rooted herb, 30-100 cm tall. It is a weed in irrigation systems and drains and in crops such as rice in 50 countries. The plant is highly adaptable in morphology and physiology to changes in the environment. Reproduction is by achenes and vegetatively by whole, immature plants and underground tubers. Seeds float easily and can be carried long distances. In Asia and Hawaii, the tubers are cultivated and eaten for their high starch and protein content.