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Submersed Plants

 
Species: Megalondonta beckii (Torr. ex Spreng.) Greene. (formerly called: Bidens beckii Torr.), water marigold
Family: Asteraceae

Water marigold is one of only a few aquatic members of the sunflower family. The underwater portions of this perennial plant have opposite, finely divided fan-like leaves, and the above water portions have simple toothed leaves. From July through September, water marigold’s yellow daisy-like flower heads are sometimes found rising above the water surface, making the plants easy to distinguish from most other aquatic species.

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Leaf: Oppositely arranged and of two types: submersed leaves are finely dissected, on short stalks, have a fan-like shape, and appear to be whorled around the stem. Emergent leaves, if present, are simple, toothed leaves that measure 2-4 cm in length and are sometimes seen floating on or rising above the water surface.

Stem: The mostly submersed stem is up to 7 m long with 8-10 cm usually extending above the water when mature.

Flower: Yellow and sunflower-like. As with all members of the sunflower family, each flower head actually consists of numerous tiny flowers, with the disk flowers forming the center of the head, and each "petal" actually representing an individual ray flower. Disk flowers are clustered in a head about 1 cm wide. Bordering ray flowers are each 1-2 cm long.

Fruit: Long (to 12 mm) and narrow, round to oval in cross section. The dark brown achenes have 3-6 needle-like bristles at the base. Numerous achenes form on each flower head.

Root: Thin and fibrous, emerging in clusters from the lower nodes of the stem.

Propagation: Seeds dispersed by water or animals.

Importance of plant: Apparently sensitive to water pollution. A food source for ducks.

Distribution: Common in northeastern and northwestern North America. Found in western and northeastern Washington and in Cascade lakes in Oregon.

Habitat: Lakeshores, ponds, and slow-flowing streams. 

May be confused with: Flowering plants may be confused with members of the genus Bidens. Water marigold can be distinguished by its submersed dissected leaves. If only the underwater leaves are present, water marigold can be confused with fanwort (Cabomba caroliniana), which has much longer leaf stalks. It also may be confused with aquatic buttercup (Ranunculus aquatilis), which has fan-shaped leaves arranged alternately on the stem, rather than oppositely. Both fanwort and aquatic buttercup have white flowers whereas water marigold has yellow flowers. 

Photographs: Megalodonta beckii plant

Line Drawings: None available 


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