Paper
Viburnum tinus is an evergreen shrub that is native to the Mediterranean region but cultivated widely in Europe and around the world. It produces ripe metallic blue fruits throughout winter [1Alkurdi M.I.S. Supuka J. Feriancová L. Bihunová M. Viburnum tinus L. as a new Mediterranean element for central Europe urban landscapes.IOSR J. Agric. Vet. Sci. 2014; 7: 50-58Crossref Google Scholar]. Despite its limited fleshy pulp [2Thebaud C. Debussche M. A field test of the effects of infructescence size on fruit removal by birds in Viburnum tinus.Oikos. 1992; 65: 391-394Crossref Scopus (16) Google Scholar], its high lipid content [3Debussche M. Cortez J. Rimbault I. Variation in fleshy fruit composition in the Mediterranean region: the importance of ripening season, life-form, fruit type and geographical distribution.Oikos. 1987; 49: 244-252Crossref Scopus (74) Google Scholar] makes it a valuable resource to the small birds [4Jordano P. Migrant birds are the main seed dispersers of blackberries in southern Spain.Oikos. 1982; 38: 183-193Crossref Google Scholar] that act as its seed-dispersers [5Debussche M. Isenmann P. A Mediterranean bird disperser assemblage: composition and phenology in relation to fruit availability.Rev. d’Ecologie. Terre Vie. 1992; 47: 411-432Google Scholar]. Here, we find that the metallic blue appearance of the fruits is produced by globular lipid inclusions arranged in a disordered multilayer structure. This structure is embedded in the cell walls of the epicarp and underlaid with a dark layer of anthocyanin pigments. The presence of such large, organized lipid aggregates in plant cell walls represents a new mechanism for structural coloration and may serve as an honest signal of nutritional content.