Nodding Bur-Marigold (Bidens cernua): yellow Minnesota wildflowers

Nodding Bur-Marigold

Plant Info
Also known as:	Nodding Beggarticks
Scientific name:	Bidens cernua
Family:	Aster (Asteraceae)
Life cycle:	annual
Origin:	native
Habitat:	sun to part shade; swamps, along shores
Bloom season:	last summer, early fall
Plant height:	6 to 36 inches
USDA PLANTS database:	Minnesota county distribution map
Spotted in Ramsey County at:	Long Lake Regional Park Rice Creek Trail Corridor Vadnais/Snail Lake Regional Park

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Flower:: Flowers are from 1 to 2 inches across, 8 oval yellow petals (ray flowers) with a point or notch at the tip, and a dull orange center. The petals may not all be the same length and occasionally are absent altogether. Each flower is at the end of a stem that arises from a leaf joint. One plant has a few to many flowers.
The bracts are long and narrow, green and curly, and unequal lengths. Between the bracts and petals is a layer of pale yellow to green sepals, about as wide as the petals, tapering to a blunt point.
Leaves and stem:: Leaves are narrow, up to 5 inches long and 1 inch wide, tapering to a point at the tip, with toothed edges and no leaf stem. Attachment is opposite, the base of the leaves may nearly surround the stem. The main stem may be green or reddish purple.
Fruit:: The flower head nods down as it ages (and is where it gets its common name) so the seed head points down. Seeds are hard and dark brown, each with 4 barbs that attach the seed to anything that brushes against it.
Notes:: Nodding Bur Marigold is commonly found on the banks of ponds and lakes in late summer and early fall. It may form large colonies, but is often scattered.