The importance of being hairy: the adverse effects of hair removal on stem photosynthesis of Verbascum speciosum are due to solar UV-B radiation.

•  Here the hypothesis was tested that hairs over photosynthetic tissues afford protection against excess radiation. •  The hair mat covering the epidermis of photosynthetic stems of Verbascum speciosum was easily removed by mild mechanical treatment. Thus, optical properties and chlorophyll fluorescence parameters were studied in the field in intact and de-haired stems, receiving ambient, ambient minus UV-B, or ambient minus total UV radiation through selective cut-off filters. •  Optical analysis indicated that de-hairing exposes underlying tissues to appreciably higher photon fluxes in the UV but slightly higher in the visible part of the spectrum. Under full solar radiation, hair removal resulted in considerable suppression of photosynthetic electron transport rates, yet this negative effect was completely abolished by excluding the UV-B radiation band. •  It is concluded that the adverse effects of hair removal on stem photosynthesis of this plant are exclusively due to UV-B radiation. This is the first field confirmation of the protective role of hairs against UV-B radiation damage.