Glochids microstructure and dew harvesting ability in Opuntia stricta (Cactaceae)

Abstract

Liquid fresh water is scarce in arid and semi-arid regions. Some organisms in these stressful habitats are well adapted to the environmental conditions and obtain fresh water directly from the atmosphere. This ability of “moisture harvesting” relies on specific microstructural features organisms exhibit at their external surfaces. In this respect, the dew harvesting ability of the arid plant species Opuntia stricta (Cactaceae) has been investigated. Its tiny stem spines, known as glochids, have a unique microstructure, ordered in hierarchical manner with an anisotropic surface. The glochids are covered with cone-shaped barbs and have dense mats of hygroscopic trichomes at the base. Dew harvesting ability in O. stricta seems to be controlled by three driving forces, namely: Laplace pressure difference, Wenzel relation and differences in wettability. The formation of special external microstructural features supporting this ability represents an adaptive trait in O. stricta to dry arid environments. Studying such structures in detail will give insights on how biomimetic inspired devices may contribute to optimize moisture harvesting in dry regions.