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Bidens beckii (Megalodonta beckii)


Water marigold colony
Water marigold in-situ

Habitat: Water marigold is found in both the emergent and submersed plant communities. It grows in soft substrates of lakes and streams, from ankle deep water to depths approaching 3 meters.

Water marigold cross-section
Stem cross-section showing two oppositely
arranged leaves, each dividing three times
where attached directly to the stem

Description: The stems of water marigold emerge from buried rootstalks and rhizomes. Two distinct leaf types are formed. The submersed leaves are finely divided, and oppositely arranged on the stem. (Note: the opposite leaves, each dividing three times where attached directly to the stem, are widely branched, and not easily distinguished from one another. This creates the appearance of a whorl of six smaller branched leaves on short leaf stems.) When preparing to flower, lance-shaped leaves with serrated margins emerge from the surface of the water on robust stalks. The emergent leaves are also oppositely arranged and attached directly to the stem. Showy, yellow, daisy-like flowers (2 to 2.5 cm wide) are produced among the emergent leaves.

Water marigold Range Map
U.S. range map of water marigold

U.S. Range:Water marigold is a native to Maine and New England, and occurs throughout much of the northern United States.

Water marigold flower
Showy yellow flowers

Annual Cycle:Water marigold is an aquatic perennial that propagates during the growing season by stem fragmentation and spreading rhizomes. If conditions are favorable, water marigold will also reproduce from seed. Fruit set is rare in the Northeast. Plants die-back to hardy rootstalks and rhizomes as winter sets in. Some stem fragments also overwinter intact. New growth emerges from stem fragments, seeds and rhizomes as the water warms in the spring. Flowers occur in midsummer, and fruit is produced by late summer.

Value to the Aquatic Community: The submersed foliage of water marigold provides shade, shelter and foraging opportunities for fish. The showy flowers attract insects. Waterfowl and shorebirds may feed upon the fruits.

Look Alikes: May be confused with other plants with finely divided leaves including bladderworts, hornworts, mermaid weeds, water crowfoots, and leafy water-milfoils.

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Water marigold flower Water marigold emergent leaves Water marigold in-situ Water marigold specimen Water marigold cross section Water marigold range map Water marigold illustration

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