|Flower heads (capitula)|
Arctium minus, commonly known as lesser burdock, burweed, louse-bur, common burdock, button-bur, cuckoo-button, or wild rhubarb, is a biennial plant. This plant is native to Europe, but is now widespread throughout most of the United States as a common weed.
Characteristics: It can grow up to 1.5 meters (1 to 5 feet) tall and form multiple branches. It is large and bushy. Flowers are prickly and pink to lavender in color. Flower heads are about 3/4 inches (2 cm) wide. The plant flowers from July through October. The flowers resemble and can be easily mistaken for thistles, but burdock can be distinguished by its extremely large (up to 50 cm) leaves and its hooked bracts. Leaves are long and ovate. Lower leaves are heart-shaped and have very wavy margins. Leaves are dark green above and woolly below. It grows an extremely deep taproot, up to 30 cm (12 in) into the ground.
Lesser Burdock produces purple flowers in its second year of growth, from July to October. Outer bracts end in hooks that are like Velcro. After the flower head dries, the hooked bracts will attach to humans and animals in order to transport the entire seedhead. 
John W. Thieret, William A. Niering, and Nancy C. Olmstead. National Audubon Sociaty Field Guide to North American Wildflowers, Eastern Region, Revised edition. Chanticleer Press, Inc, 2001. ISBN 0-375-40232-2 Richard H. Uva, Joseph C. Neal, and Joseph M. Ditomaso. Weeds of the Northeast. Cornell University Press, 1997. ISBN 0-8014-8334-4
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