The most important application of Fibonacci fractions is in botany: plants arrange the leaves on their stems (phyllotaxy) in many different ways, but “only those conforming to a Fibonacci fraction allow for efficient packing of leaf primordia on the meristem surface.” There is also an application in optics.
R. W Pearcy & W Yang ``The functional morphology of light capture and carbon gain in the Redwood forest understorey plant Adenocaulon bicolor Hook'' Functional Ecology12 4 (1998): 551
H. C. Rosu, J. P. Trevino, H. Cabrera & J. S. Murguia, ``Self-image effects for diffraction and dispersion'' Electromagnetic Phenomena6 2 (2006): 204 - 211