Leaf hairs of A. populifolia, a tropical and subtropical coastal dune pioneer, transmitted 83 ± 2 % of light incident on the leaf. Hairs absorbed strongly at wavelengths below 350 nm, but at a low uniform value at the longer wavelengths. At high irradiances, removal of leaf hairs resulted in photosynthetic rates (A) that were lower than when leaves were left with hairs, but had incident PAR corrected to the intensities transmitted through to the leaf surface. The reduction in A of leaves with hairs removed was associated with increased non-radiative energy dissipation. The hair layer increased leaf diffusion resistance to water loss, leading to a reduction in transpiration (E) and higher instantaneous water use efficiency of leaves with an intact hair layer at all light intensities measured. The lower transpiration rates of leaves with hairs gave rise to higher leaf temperatures, despite the reduced radiation load on these leaves. Similar effects of the hair layer on A, E and leaf temperature were found in the field as well as under controlled conditions. The influence of the hair layer on photosynthesis was probably via a reduction in photoinhibition (consequent upon the reduction in UV radiation incident of the leaf surface) rather than any effect on leaf conductance to gas exchange or on leaf temperature.