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A Tree Leaf's Shape, Margin and Venation


The way a leaf looks in terms of leaf shape, leaf margin, leaf arrangement and leaf venation is important for identifying plants to include trees. These structures are always species specific and will consistently grow to a genetically determined pattern and shape. Botanists and foresters have developed terms for these patterns and shapes which help in tree identification. Some tree species make things more interesting by displaying more than one type of leaf structure.


1. Leaf Shape and Arrangement

Wikimedia Commons/derivative work: McSush

Studying leaf shape and the arrangement of leaves on a stem is the most widely used way of identifying a tree in the field during the growing season. The novice taxonomist usually starts with a tree leaf shape which is determined by the presence or absence of lobes. One can often can name the tree species without using any other identification marker.

One thing to remember is that a tree's leaves can also vary in shape according to its position on the tree, its age after budding, the location of its twig on the tree and insect/disease leaf damage damage. These variations are usually easy to deal with by finding a healthy specimen in its natural environment.

2. Leaf Margins

Wikimedia Commons/derivative work: McSush

All tree leaves exhibit margins (leaf blade edges) that are either serrated or unserrated. Serrated leaves have "teeth". These toothed leaf margins serve as valuable markers for identification when comparing their patterns, sizes and shapes. Unserrated leaves have no teeth and are described as being "smooth".

3. Leaf Venation

Wikimedia Commons/derivative work: McSush

Leaves have unique structures, called veins, that transports liquids and nutrients to leaf cells. Veins also carry the products of photosynthesis back to the rest of the tree. A tree leaf has several types of veins, the basic central one called the midrib or midvein. Other veins connect to the midrib and have their own unique patterns. A leaf can be symmetric or asymmetric off the midvein.

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