Variegated leaves are common in forest understorey species. As sunflecks (patches of direct sunlight) pass over the leaves the plant is exposed to rapid, dynamic changes between deep shade and high intensity light. The different zones of the leaf interact differently with high or low light intensities. The pale regions perform photosynthesis best at high light (in sunflecks) and the dark regions maximise photosynthesis in the shade. In this way some part of the leaf can perform photosynthesis well no matter how the light changes.

In this example, purple cyclamen (𝘊𝘺𝘤𝘭𝘢𝘮𝘦𝘯 𝘱𝘶𝘳𝘱𝘶𝘳𝘢𝘴𝘤𝘦𝘯𝘴: Primulaceae) grows in the understorey of woodland at Monte Barro, Italy. 𝘊𝘺𝘤𝘭𝘢𝘮𝘦𝘯 𝘱𝘶𝘳𝘱𝘶𝘳𝘢𝘴𝘤𝘦𝘯𝘴 has two regions of the leaf that interact differently with light. The pale regions have air spaces under the outer, epidermal, layer which form a reflective ‘blister’ (inside the leaf, the cells are rounder, letting air pass around them). This is associated with low chlorophyll pigment contents and also a lack of red pigment (anthocyanin) in the lower epidermis. This pale region performs photosynthesis most effectively when direct, bright, white sunlight passes over the leaf, reflecting excess light or letting it pass through, and leaving just enough for effective photosynthesis. However, in the shade the pale regions do not have enough chlorophyll to scavenge light, and photosynthesis is minimal. The dark areas have closely packed cells with high chlorophyll contents, which can intercept the scarce photons of light that are available in the shade. Also, the cells of the lower epidermis in these regions have high anthocyanin contents, which reflects red light back up into the leaf, giving the chlorophyll a second chance to absorb it (the ‘red mirror’ effect). While these are effective mechanisms in the shade, the dark regions become over-exposed in the sunflecks, with excessive energy being absorbed and hindering photosynthesis (an effect known as photoinhibition). Having two regions of the leaf optimised for high or low light means that there is always some part of the leaf that is able to photosynthesise, even though the light changes throughout the day or under different weather conditions.

𝗧𝗵𝗶𝘀 𝗰𝗵𝗮𝗻𝗻𝗲𝗹 𝗶𝘀 𝗻𝗼𝘁 𝗺𝗼𝗻𝗲𝘁𝗶𝘇𝗲𝗱.

𝗦𝗰𝗶𝗲𝗻𝘁𝗶𝗳𝗶𝗰 𝗹𝗶𝘁𝗲𝗿𝗮𝘁𝘂𝗿𝗲:
Klančnik, K., Levpušček, M. & Gaberščik, A. (2016) Variegation and red abaxial epidermis define the leaf optical properties of 𝘊𝘺𝘤𝘭𝘢𝘮𝘦𝘯 𝘱𝘶𝘳𝘱𝘶𝘳𝘢𝘴𝘤𝘦𝘯𝘴. Flora, 224: 87-95. https://doi.org/10.1016/j.flora.2016....

Pierce, S. (2003) Variegated foliage and photosynthesis. Journal of the Bromeliad Society, 53(5): 216-240. https://www.researchgate.net/publicat...

Zhang, J.-H., Zeng, J.-C., Wang, X.-M., Chen, S.-F., Albach, D.C., Li, H.-Q. (2020) A revised classification of leaf variegation types. Flora, 272: 151703. https://doi.org/10.1016/j.flora.2020..... https://tiantong.ecnu.edu.cn/kindedit...