Opposite leaves usually have the adjacent tiers cross at right angles to minimize overlap. This maximizes availability of sunlight and air. The arrangement of the leaves minimizes the overlap between one leaf and another. Whorled – leaves occurring three or more on a single node. Opposite – leaves occurring in pairs at the nodes.Īlternate – leaves staggered or not directly across from each other. Leaves can be arranged on a twig in one of three ways ( Figure 3): However, the ones mentioned are some very common, simple shapes. There are other leaf shapes, depending on the source used. Lance leaves are much longer than they are wide (typically 4x longer), and although generally the same width throughout, they may be slightly wider in the middle. Like the heart shaped leaves, the triangular leaves look as the name implies – the leaf is in the shape of a triangle. Ovate leaves are broadest below the middle and longer than they are wide. Elliptical leaves are broadest in the center and taper near the ends. Obovate leaves are broadest above the middle and longer than they are wide. Heart shaped leaves look exactly as the name implies – the leaf is in the shape of a heart ( Figure 2). The shape of the leaf has therefore developed over time to balance these needs: maximizing sunlight but minimizing heat absorption and/or water loss. In this process, the leaf also receives heat.
A leaf’s task is to capture sunlight for photosynthesis, producing food for the tree. The shape gives the tree its best chance of survival based on the environmental factors in the ecosystem. The shape of a tree’s leaves form over the course of a tree species’ evolutionary history. Because these needles last several years on a tree while broadleaves only live for one growing season, trees with needles have an advantage over broadleaf trees, in that the metabolic cost of leaf production can be recovered with photosynthesis over several growing seasons. Trees with needlelike leaves are well suited to sites where water conservation is very important for survival. Needlelike leaves also have a thick coating to prevent excessive water loss. Needlelike leaves have very little surface area therefore, they are not able to capture much sunlight for photosynthesis. Generally, these leaves stay on the tree for more than a year. Trees like pines and spruces have needlelike leaves, and trees like junipers and cedars have scalelike leaves. These have needlelike or scalelike leaves. The other type of tree is an evergreen tree. Mostly, these trees are deciduous and drop their leaves in autumn. These trees have leaves with wide blades exposing a large surface area for photosynthesis ( e.g. These include leaf shape, leaf arrangement, and leaf margins.īroadleaf trees are very common in the United States ( Figure 1). There are many clues to look for on a leaf to help identify the tree from which it came. Leaves are very characteristic of a particular tree species. Examining leaves is one of the most common ways to identify trees.
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