We associate red leaves with the fall, but every photograph in this post was taken this spring. These plants don’t stay red, they turn green, but why do they start off this way?
No-one knows, but a recent suggestion is that the “juvenile reddening”makes the tender young leaves less discernible to some insects that might devour them, and the associated chemicals make them unpalatable.* Below is a hawthorn:
And a beech:
All sorts of plants start like this. Here is a Wild Sarsaparilla:
And here is a fern:
The phenomenon is found not only in many trees, like this maple:
but also in many tiny plants, like this miniscule fern:
And then the red leaves turn green, and the flowers appear. Hard to believe this Striped Maple is the same plant as the one in the very first photo:
*A little more science. The chemical that makes the leaves red (in fall or spring) is called Anthocyanin, and the tree uses energy to produce it, so it must serve some beneficial purpose. It seems to be more common in young trees than in mature ones, and in poor soils. It may protect somewhat against drought, and late frosts. One theory was that it acted as a sunscreen, but recent work has debunked that idea, leaving the insect-deterrent effect as the leading contender for now.
“Compared with red phenotypes, green phenotypes suffered greater herbivore damage, as judged by the number of leaves attacked and the area lost to herbivory. .. The decreased reflectance in the green spectral band and the concomitant leveling of reflectance throughout the 400-570 nm spectral range may either make red leaves less discernible to some insect herbivores or make insect herbivores more discernible to predators, or both. Moreover, excessive herbivory may be additionally discouraged by the high phenolic concentrations in red leaves.”