Mechanics of water collection in plants via morphology change of conical hairs

In an arid area like the Namib Desert, plants and animals obtain moisture needed for life from mist in the air. There, some plants have hairs or fibrous structures on their leaf surface that reportedly collect fresh water from the air. We examined the morphology and function of leaf hairs of plants during water collection under different circumstances. We studied the water collecting mechanics of several plants having fibrous hairs on their leaves: tomato, balsam pear, Berkheya purpurea, and Lychnis sieboldii. This plant was selected for detailed investigation as a model because this plant originated from dry grassland near Mount Aso in Kyusyu, Japan. We found a unique feature of water collection and release in this plant. The cone-shaped hairs having inner microfibers were reversibly converted to crushed plates that were twisted perpendicularly in dry conditions. Microfibers found in the hairs seem to be responsible for water storage and release. Their unique reciprocal morphological changes, cone-shaped hairs transformed into perpendicularly twisted shapes, depend on the moisture level in the air, and water stored during wet external conditions was released onto the leaf in drier conditions. These morphological changes were recorded as a movie. Simulations explained the formation of the twisted structure. In theoretical analyses, twisted structures were found to give higher mechanical strength. Similar phenomena were found in the other plants described above. These findings pave the way to new bioinspired technology for alleviating global water shortages.