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White Mule's-ears Xanthium strumarium


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White Mule's-ears - flowers
credit: Robert H. Mohlenbrock

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Alternate name: Rough Cockleburr

Family: Asteraceae, Aster view all from this family

Description Rough-stemmed plant with separate greenish male and female flower heads.
Habit: native annual herb; coarse-textured, with erect, branched, usually hairy, stems; fibrous roots.
Height: 4-32 in (10-80 cm) or more.
Leaf: alternate, on long stalks, round to deltate, pointed, sometimes shallowly palmately 3-5-lobed, heart-shaped base, toothed, hairy, 1.5-7 in (4-18 cm) long or more, nearly as wide.
Flower: Male and female flowers borne separately in small heads; each male head subtended by a series of small green bracts; each female head subtended by hooked prickles.
Fruit: thick dry seed, embedded in prickly bur; .4-1.2 in (10-30 mm) long or more.

Warning Seeds and seed leaves can be toxic to animals if eaten. Humans should generally avoid ingesting plants that are toxic to animals. Foliage can cause skin irritation in humans.

Flower July to October.

Habitat Damp or seasonally wet sites, often with alkaline soils: fallow fields, streambanks, sloughs, wet prairies, waste places, disturbed sites, roadsides, low ground, margins of agriculture; 30-6500 ft (10-2000 m).

Range Native to North America, now naturalized in 49 states, southern Canada, and Europe.

Discussion Also known as rough cockleburr, common cocklebur, large cocklebur. Three varieties are recognized. Considered weedy or invasive in many areas; listed as a noxious weed in Arkansas and Iowa.

The only other species of this genus occurring in North America is Spiny Clotbur (X. spinosum), which has tapering, shiny, veined leaves and distinctive 3-branched orangish spines at the point of each leaf attachment. A cocklebur was the inspiration for a Swiss engineer, George deMastral, in 1948, for the invention of Velcro. He examined the burs that stuck to his socks and discovered that they consisted of hundreds of tiny hooks, which attached themselves to anything loopy.