Leaf epidermal water-absorbing scales and their absorption of unsaturated atmospheric water in Reaumuria soongorica, a desert plant from the northwest arid region of China

•A specific leaf micro-structure – WASs in desert plant Reaumuria soongorica.•WASs can absorb unsaturated atmospheric water (UAW).•The micro-structure morphological change of WASs under high relative humidity.•The chemical composition the valves of WASs contribute to absorb UAW.

This study found water-absorbing scales (WASs), which could absorb unsaturated atmospheric water (UAW), in the leaves of Reaumuria soongorica, a super-xerophytic desert plant. WASs were a complex cellular structure surmounted by four to seven valves that formed an inverted cone pore. The base of the cone comprised three or four flat, thin-walled, living cells. Under low humidity, the valves of WASs contracted, becoming nearly closed and leaving a small central opening, thus forming a more or less impermeable lid. Under high humidity, the valves of WASs absorbed UAW from the atmosphere and swelled, gradually expanding and forming a larger central opening. The basal cells raised the lid of the scale and allowed water to flow by capillary action over the cuticle. At a relative humidity of 75–95% with a wetting period of 3 h in duration, the valve opened fully, the central opening expanded to form a polygonal structure, and the water content of the leaves increased from 47.8% to 54.2%. An EDS analysis with a scanning electron microscope found more chloride, sulfate and potassium in the valves of WASs than in normal leaf epidermis. This chemical composition may facilitate the absorption of water from unsaturated air by WASs.