USA NPN National Phenology Network

Taking the Pulse of Our Planet

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sun leaves

Sun leaves and shade leaves are common in plant canopies, with sun leaves located on the top and outer, unshaded perimeter of the plant and shade leaves located on the shaded sides of the plant, under the sun leaves within the canopy.
Shade leaves receive less sunlight (photosynthetically active radiation) than sun leaves. As a result of their position within a canopy, individual leaves respond by developing slightly differently (called plasticity) but suited to their position within the canopy: morphologically, anatomically and metabolically. All this leaf variation, within one plant, results in maximizing a plant’s net rate of energy capture.
Shade leaves differ morphologically by being larger, less deeply lobed (if the species has lobed leaves), and thinner, and can have a deeper green coloring and a different texture than sun leaves on the same plant. Anatomically, sun leaves are thicker by having more or thicker palisade mesophyll cell layers with longer cells, a less developed spongy mesophyll, and a thicker cuticle than shade leaves.  Shade leaves contain more chlorophyll (chloroplasts) within their thinner layer of mesophyll cells, resulting in an increased ability to harvest sunlight at low radiation levels.

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