How do burdock and cocklebur use hooks to disperse their seeds?

Burdock (Arctium) and cocklebur (Xanthium strumarium) are members of the Asteraceae family that utilize a method of seed dispersal known as epizoochory, where plants rely on animals to inadvertently transport their seeds.12

In both of these plants, the protective bracts surrounding the developing flower head—collectively known as the involucre—are equipped with hooks. When an animal or human brushes against the plant, these hooked structures latch onto fur or clothing, allowing the entire seed-bearing head to be distributed intact as the carrier moves to a new location. This functional adaptation ensures the seeds are carried away from the parent plant, facilitating their spread across wider areas. The design of the burdock’s hooked head is notably recognized for having inspired the invention of Velcro.21