A burr is a dry fruit or seed pod covered in microscopic hooks, spines, or stiff hairs. These structures are a highly effective mechanism for plants to spread their seeds across large distances. This process, known as zoochory, is seed dispersal by animals.
The Biological Mechanism of Burrs
The remarkable ability of burrs to cling comes from a specific biological architecture, essentially a natural hook-and-loop fastener. The burr’s surface is covered with tiny, rigid projections that terminate in a minute, curved hook. These hooks easily snag onto the fibrous loops of clothing or the fine hairs of animal fur.
This method of seed transport, called epizoochory, is a highly successful evolutionary strategy. The burr detaches easily from the parent plant and attaches firmly to a moving host, allowing seeds to be carried far from the original location. The Swiss engineer who invented Velcro was inspired by how burdock burrs clung to his dog’s fur after a hike.
The strength of the attachment depends on the burr’s size and the flexibility of its hooks, allowing it to penetrate and hold tight against various surfaces. By traveling on an animal or person, the seeds are transported to a new area for germination. The plant benefits from colonizing new territory.
Identification of Common Burr-Producing Plants
One well-known burr producer is Common Burdock (Arctium minus), a biennial plant introduced to North America from Europe. Its mature burrs are spherical, about one inch in diameter, and covered in stiff, hooked bristles. These plants are often found in disturbed soils, along roadsides, and in uncultivated pastures.
Another common culprit is the Cocklebur (Xanthium species), which produces a hard, egg-shaped fruit covered in numerous stout, hooked spines. Cockleburs thrive in moist environments, such as riverbeds and cultivated fields. The spines on these burrs can be tough and sometimes cause injury or irritation to animals.
Beggar’s-lice or Sticktights (Desmodium or Bidens species) are smaller plants that create tiny, flat, segmented seed pods. These pods are covered in fine, hair-like hooks that easily cling to clothing and pet fur, giving the plant its common name. They are found in wooded areas, thickets, and fields, sticking to anything brushing past them.
Sandburs (Cenchrus species) are a type of grass that produce small, sharp-pointed burrs, often a nuisance in lawns and sandy soil. These star-shaped burrs can penetrate skin or thin shoes, and they are troublesome in weakened or neglected turf. Proper identification is important because the size and shape of the burr varies among species.
Practical Strategies for Burr Removal and Control
Removing burrs from clothing requires methods that avoid driving the hooks deeper into the fabric fibers. For tightly woven materials, duct tape pressed firmly onto the burrs and quickly peeled off can lift them. A fine-toothed comb or a stiff-bristled brush, used with a light touch along the grain of the fabric, can also gently work them out.
When dealing with pet fur, first saturate the affected area with water or a detangling product. This lubrication helps the burrs slide out of the hair, preventing excessive pulling on the skin. A slicker brush or a metal flea comb can then be used to gently tease the burrs out, starting from the outside of the mat and working toward the skin.
To control burr-producing plants, the most effective strategy is to prevent the plant from going to seed. This means manually pulling the weeds before the mature burrs form, typically in late summer or early fall. Any pulled plants containing mature burrs should be disposed of in a sealed container rather than composted, preventing the seeds from spreading.