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REPRINTED FROM TECHLINENEWS.COM JUNE 2017 Have Burs Will Travel Cocklebur or Burdock—What’s the Difference?

By Celestine Duncan PHOTO BY THINK LIKE A HORSE

Common cocklebur (Xanthium strumarium L.) and common burdock (Arctium minus) are members of the sunflower family. Both plants have bur-like seed heads that are easily spread by clinging to human clothing, and fur of domestic animals, wildlife, and livestock. Although the plants share similar habitat and are both widely distributed across the United States and southern Canada, cocklebur tends to flourish in warmer regions than burdock (Figure 1).

FIGURE 1. DISTRIBUTION OF COMMON COCKLEBUR (LEFT) AND COMMON BURDOCK (RIGHT) IN THE UNITED STATES (EDDMAPS 2017). ABOUT TECHLINE TechLine Invasive Plant News Cocklebur is native to the United States and is primarily a weed of riparian areas, pastures, disturbed areas aims to provide an objective communication tool for on-the- and cultivated cropland. Burdock is introduced from Eurasia and likely reached North American with early ground natural resource managers who face common management English and French settlers. It was considered ‘widespread’ in Pennsylvania by the mid 1800s and is now challenges so they may share the successes of their programs and naturalized throughout North America. It is found primarily in riparian sites, pasture margins and natural learn from one another. areas; however, it is not problematic in cultivated land. Print newsletters are published twice per year and delivered free of charge. Issues can be downloaded Common cocklebur and burdock differ in their life cycle, growth form, flower type and seed heads. The from www.techlinenews.com. Editor, Celestine Duncan following information compares differences between the two weeds. Copy Editor/Design, Kaaren Robbins Contact: [email protected]

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Cocklebur (far left): Annual plant that germinates and produces seed the same year. Photo by John M. Randall, The Nature Conservancy, Bugwood.org.

Burdock (left): Biennial (sometimes short-lived perennial) plant that germinates and spends the first growing season as a rosette, producing a flower stalk and seed the second growing season. Photo, Ansel Oommen, Bugwood.org.

Growth Form

Both weeds are tap rooted; however, burdock is more robust with larger leaves.

Plant Height Cocklebur: two to four feet tall

Burdock: from three to more than six feet tall depending on growing conditions.

Leaves Both weeds have alternate, triangular to heart-shaped leaves with petioles (leaf stalks) Cocklebur (top left): Leaves are about two to six inches long and both surfaces are covered with minute hair-like projections that are rough to the touch. Leaves have three prominent veins on the upper surface of the leaf that arise from the same point. Photo, University of Massachusetts Extension.

Burdock (bottom left): Leaves are dark green above and whitish green and woolly/hairy beneath with margins that are toothed or wavy. Basal leaves are large, up to 14 inches across and 18 inches long, resembling rhubarb. Lower leaves may have hollow stems. Photo, Theodore Webster, USDA Agricultural Research Service.

Stems

Cocklebur (far left): Plants have purple or black markings on stem. Photo by Jack Kelly Clark, Univ. California.

Burdock (left): Stems are thick and ribbed, without purple or black marks. Photo, G. D. Bebeau.

Flowers

Cocklebur (far left): Separate male and female flowers are brownish white and green, respectively. Male flowers are uppermost on the plant axis. The seed pod or bur is one complete flower head containing 2 female flowers. Flower heads form in leaf axils and at the ends of branches. Photo, John M. Randall, The Nature Conservancy, Bugwood.org.

Burdock (left): Perfect flowers (both male and female parts) that are lavender to pink. Flower heads form in leaf axils and at the end of branches. Individual tubular flowers are surrounded by bracts and hooked spines making the seed head into a bur. Photo, USDA, University of Massachusetts Extension.

Seed pod (burs)

Cocklebur (far left): Bur is green to dark brown in color and contains two black, flattened, ribbed seeds. Burs are football-shaped, about 0.5 to 1 inch long x 0.3 to 0.6 inches wide, covered with hooked prickles. There are two curved spines at the tip of each bur.

Burdock (left): Each seed pod or bur is grayish green to light brown, ball shaped about 0.5 to 1 inch in size, and contains from 20 to more than 40 seeds. Photo, Celestine Duncan.

2 | HAVE BURS WILL TRAVEL—COCKLEBUR OR BURDOCK—WHAT’S THE DIFFERENCE?