A flowering Fenestraria rhopalophylla, so named due to the translucent leaf window on the tips of its modified leaf.
Leaf window, also known as epidermal window,[1] and fenestration,[2][3] is a specialized leaf structure consisting of a translucent area through which light can enter the interior surfaces of the leaf where photosynthesis can occur. The translucent structure may include epidermal tissue, and in some succulent plants it consists of several cell layers of parenchyma, which may also function as water-storage tissue.[4] It can appear as a large continuous patch, a variegated or reticulated region, or as numerous small spots. It is found in some succulent plants native to arid climates, allowing much of the plant to remain beneath the soil surface where it is protected from desiccation by winds and heat while optimizing light absorption. Many species featuring leaf windows are native to Southern Africa.
Functions
The primary function of the translucent windows is to increase the absorption of radiant energy, and thereby the rate of photosynthesis.[5] Epidermal windows are commonly situated at the apex of leaves, allowing light to be captured and utilized even when the plant is almost entirely below the soil surface,[6] minimizing exposure of leaf surface area to desiccation by intense heat. The windows focus and channel diffused light to the green photosynthesizing surface hidden inside the underground part of the plant.[1] An absence of stomata in the translucent tissue prevents water loss. It has been found in the Lithops species of succulents that leaf window size correlates inversely with habitat solar irradiance; plants growing in regions of high irradiance and low rainfall have smaller windows than those growing in cloudy, high-rainfall regions.[7]
Plants with leaf windows are sometimes known as window plants, though this is also the common name used to refer to Fenestraria rhopalophylla.[citation needed]
