UC Davis

Land plants exhibit a wide variety of defences that deter the consumption of leaves and stems, including trichomes (hairs), thorns, and thick cuticles. In many plants, trichomes are hooked or inclined to the leaf or stem surface, and the teeth on leaf margins point either apically or more rarely toward the base. The role of these anisotropic structures as potential defences has been largely ignored. In the present study, it is proposed that apically oriented surface features function as ratchets directing the movements of small herbivores toward the leaf ends and ultimately off the leaf, whereas basally oriented protrusions interfere with the ascent of consumers to the upper parts of the plant. These proposed defencive functions do not exclude other potential benefits of anisotropic features, such as self-cleaning of surfaces. The proposed defencive role of apically oriented trichomes and teeth may represent an unusual class of physical defences that speed up rather than slow down encounters between enemies and their plant victims.