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Washington State Department of Ecology > Water & shorelines > Freshwater studies > Lake water quality > Aquatic Plant Guide home > Submersed Plants > Ruppia maritima and Ruppia cirrhosa

Aquatic Plant Identification Manual for Washington's Freshwater Plants

Submersed Plants

Species: Ruppia martima L., widgeongrass
Ruppia cirrhosa (Petag.) Grande, ditch-grass
Family: Ruppiaceae

Widgeongrasses are bushy, fan-like underwater plants (occasionally the flowers may extend above the water) with slender grass-like leaves attached to sheathing bases. They are freshwater species with a high salinity and alkalinity tolerance. They can be perennials or annuals and are highly variable in form depending on environmental conditions. Some botanists believe that R. maritima and R. cirrhosa are a singe variable species with most differences in appearance related to habitat. 
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Leaf: Long, narrow, alternate leaves are less than 1 mm wide. Stipular sheaths, less than 7 cm long, are completely fused to the leaf and often broadly clasp the stem. R. maritima: leaves to 10.5 cm long. R. cirrhosa: leaves to 45 cm long. 

Stem: Many branched stems, to 0.5 m long, less than 1 mm wide, root at the nodes and often have a zig-zag appearance. Produces slender horizontal rhizomes.

Flower: Tiny flowers (3-5 mm across), lack petals and sepals, and occur in pairs on stalks. Pollination often occurs underwater or at the waters surface. Once pollinated, the flower stalk coils.

Fruit: Dark colored, egg to pear-shaped, symmetrical to highly asymmetrical achene is 1.5 to 2 mm long and occurs in a cluster. Each fruit is on individual stalks, but all are connected to a long flowering stalk (peduncle). R. maritima: peduncle 0.2-2 cm, less than 3 coils. R. cirrhosa: peduncle 3-30 cm, more than 5 coils.

Root: Fibrous. From lower nodes of erect stems and shallowly buried rhizomes.

Propagation: Seeds, fragments, rhizomes; occasionally produces overwintering buds. 

Importance of plant: Provides cover and food for many aquatic species. All the plant parts are eaten by waterfowl (over 5,000 seeds were found in one duck). Often used for habitat rehabilitation.

Distribution: Worldwide.

Habitat: Ruppia maritima: mostly a coastal species found in brackish water and will tolerate tidal exposure. Ruppia cirrhosa: mostly an inland plant found in alkaline lakes.

May be confused with: Each other. Penducle length is the most consistently different physical characteristic; habitat also helps. R. maritima is usually in coastal salty water, and R. cirrhosa is usually in inland alkaline water. When not in flower or fruit, they closely resemble sago pondweed (Potamogeton pectinatus), but sago pondweed has stipules that are not completely fused to the leaf. 

Photographs: Closeup of Ruppia maritima 

Line Drawings: Ruppia

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