These findings suggest that floral traits and phenology would be favoured to attract bird pollinators in cold weather, in which insect activity is limited.

In many plants, leaves that are young and/or old (senescent) are not green. One adaptive hypothesis proposed that leaf color change could be a warning signal reducing insect attack. If leaf coloration involves less herbivory, it remains unclear why leaves in many species are constantly green. To examine whether green leaves reduce herbivory by physical defense as an alternative to the supposed warning signal of red leaves, we conducted comparative analyses of leaf color and protective tissues of 76 woody species in spring. Th e protective features (trichomes, enhanced cuticle and multiple epidermis) and the distribution of red pigments within leaves were examined in both young and mature leaves. We observed that redness was more frequent in young leaves than in senescent leaves. Compared to 36 species with red young leaves, 40 species with green young leaves showed a signifi cantly higher incidence of enhanced cuticle and trichomes in both phylogenetic and non-phylogenetic analyses. Th e phylogenetic analysis indicated that the multiple origins of mechanical protection were generally associated with loss of red coloration. Our fi nding of relatively poor mechanical protection in red young leaves provides additional evidence for the adaptive explanation of leaf color change.

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