Tree Leaf Margins: Toothed and Entire: Tree Leaf Key

Serrated edges appear to have helped trees adapt to cold climates

Detailed shots of serrated leaves on an Elm tree

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When narrowing down a type of tree based on its leaf shape, you'll look at leaf characteristics: overall shape, whether it is one leaf or has lobes or leaflets, serration, and direction of its veining. To determine if a leaf is toothed (serrated) or entire (smooth), you'll look at what is called the leaf margin (the outside edge of the leaf). If it's a serrated leaf, it's more likely to be from a cooler climate and a deciduous forest. The toothed leaves lose more water than smooth-edged leaves, so leaves are going to be less serrated on trees in drier climates.

Why Have Serrated Leaves?

Closeup of a green nanking cherry leaf.

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Researchers studying plants have noted that trees with serrated edges are not often found in tropical rainforests but in deciduous forests, and so they have studied whether it's an adaptation that helps the plant adjust to light, water, predators, or temperature/growing season length. For one, they have found that leaves with teeth have better transpiration and photosynthesis early in the growing season while leaves are starting out than those with smooth-edged leaves. Being able to kick into gear quickly early in the season has helped these trees function in the colder climates, because water loss through leaves moves sap throughout the tree. This brings energy to the leaves, and they can maximize their unfurling and growth rates right away. 

Because the leaves essentially feed the tree through photosynthesis, it's to the tree's advantage to get the leaves growing quickly and making food. The trees also need to be efficient during the shorter growing season. Cold temperatures limit a plant's photosynthesis, so if the plant can overcome that through serrated leaves, it's to its benefit to grow them that way.

Correlation With Temperature

Brown Hazel tree leaf in the winter covered with snow.

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The higher number of serrations of the leaves, how big the serrations are, and how deep the serrations are all correlated with lower-temperature climates. Even trees in the same species grown in different areas of the country will have their leaves develop differently, with more jagged edges and more teeth in cooler areas, as found in a study that planted the same types of trees in gardens in Rhode Island and Florida.

The correlation between climate and serration on leaves also has helped people studying fossils of plant life to understand the contemporaneous climate where a fossil was found. Leaf margins are also an area of study for people looking into climate change and how trees manage to adapt to changing conditions.

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Unlobed Leaf Without Teeth

Smooth edges of Magnolia leaves.

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Does your tree have a leaf that is smooth around the entire margins of the leaf? If yes, go to tree leaves without teeth in the Tree Leaf Key. The possible trees it could be include the magnolia, persimmon, dogwood, blackgum, water oak or live oak.

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Unlobed Leaf With Teeth

Green toothed leaves on an Elm tree.

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Does your tree have a leaf that is serrated and toothed around the margins of the leaf? If yes, go to tree leaves with teeth in the Tree Leaf Key. Possible trees that your leaf could belong to include members of the elm, willow, beech, cherry, or birch tree families.