The wooly hairs of the alpine edelweiss protect the plant's cells from ultraviolet radiation by acting as photonic structures that interact with and absorb the UV radiation.

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"Want to protect yourself from sun damage? Slathering yourself in edelweiss could help. Edelweiss is a mountain flower and so is exposed to a large amount of ultraviolet light. Just how it protects itself from tissue damage at such high altitudes has been a mystery, says Jean Pol Vigneron at the University of Notre-Dame de la Paix in Namur, Belgium. Vigneron and his colleagues measured the spectrum of light reflected from the plants and found that while most wavelengths are reflected, UV is not. 'It's astonishing, but the plant completely absorbs the UV,' says Vigneron. The team then examined the tiny, white hairs that cover edelweiss leaves under a scanning electron microscope. They found that the hairs are made up of parallel fibres 0.18 micrometres across, which is close to the wavelength of UV light. This means they can interact with UV light, steering it along the length of the leaves, says Vigneron. In this way, the UV light is absorbed over a large number of hairs instead of penetrating to the plant's body. The trick should be exploited to create a 'natural' sunscreen for people, says Vigneron. 'We currently use sunscreens made of titanium dioxide particles, but these can be absorbed through the skin and can be harmful,' he says." (New Scientist 2007) Edit Summary


"The filaments forming the hair layer have been found to exhibit an internal structure which may be one of the few examples of a photonic structure found in a plant. Measurements of light transmission through a self-supported layer of hair pads taken from the bracts supports the idea that the wooly layer covering the plant absorbs near-ultraviolet radiation before it reaches the cellular tissue. Calculations based on a photonic-crystal model provide insight on the way radiation can be absorbed by the filamentary threads." (Vigneron et al. 2005:011906-1)

Journal article
Optical structure and function of the white filamentary hair covering the edelweiss bracts

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Magazine article
Slap on the edelweiss for the ultimate sunscreen--

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