Mucilage reduces leaf herbivory in Schreber’s watershield, Brasenia schreberi J.F. Gmel. (Cabombaceae)
Insect herbivores negatively affect plants by consuming biomass that could otherwise be used for growth or reproduction. To reduce their impact, plants have evolved a wide range of antiherbivore defenses. Schreber’s watershield (Brasenia schreberi J.F. Gmel.; Cabombaceae) is a freshwater, aquatic plant that produces a thick mucilage on the underside of leaves and all underwater organs. The mucilage has been proposed as a mechanism of defense against herbivory, but this hypothesis is untested. We conducted a comparative study to determine whether the quantity of mucilage on the underside of leaves is associated with herbivore damage on the leaves. We found that leaves with the thickest mucilage layer were the least damaged. To determine whether mucilage is directly responsible for defense against herbivores, we conducted a manipulative study where we removed the mucilage from the abaxial surface of leaves. We found that demucilated leaves experienced higher amounts of herbivore damage than leaves with their mucilage left intact. We conclude that the mucilage produced by B. schreberi functions to reduce herbivory on leaves, although its association with underwater herbivores and its specific antiherbivore properties remain unknown.