Carotenoids are a class of pigments found in some plants, imparting various shades of yellow, orange, or red. They make corn yellow, carrots and pumpkins orange, and tomatoes red. And in the fall, they add to the bounty of resplendent warm tones. While anthocyanins offer protection from UV radiation, carotenoids primarily serve as accessory pigments that extend the range of light chloroplasts can use for photosynthesis. As such their concentration within the plant remains relatively constant throughout the growing season. Leaves don’t appear orange in the summer, however, because the abundant green of chlorophyll overwhelms and masks the yellow pigments. As chlorophyll begins to break down in the fall, the underlying yellows are revealed. And the displays can be stunning.
In the leaves of our trees, carotenoids tend to be a golden yellow. When carotenoid-rich trees – sugar maples, big-toothed aspens, tulip poplar, etc. – begin to produce red to purple anthocyanins in the fall, the colors blend into a vibrant orange tone. Trees that produce carotenoids but lack anthocyanins (notably quaking aspens, the hickories) take a striking golden yellow color in the fall.