ID a Tree Using Leaf 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 all 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. Other tree species leaves make it nearly impossible to misidentify because each leaf is so unique. Trees with unique leaves include ginkgo, sassafras, yellow poplar and mulberry.

The function of a tree's leaf is not determined by the above characteristics but is a precious package of cells, pores and vascular tissue that facilitate the movement of oxygen, carbon dioxide, and water vapor supporting the process of photosynthesis. More about this at Anatomy and Biology of a Tree Leaf.

Also, all tree leaves have an outer layer called the epidermis which can be used in the identification process. This leaf "skin" always has a waxy cover called the cuticle and varies in thickness with every tree species. The epidermis may or may not support leaf hairs which can be an important botanical identifier.

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Leaf Shape and Arrangement

Leaf Shapes and Arrangements. 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 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 so be careful. These variations are usually easy to deal with by finding a healthy specimen in its natural environment.

  • Leaf shape can vary considerably - the most common shapes have names including oval, truncate, elliptical, lancolate, and linear. Leaf tips and bases can also be unique with names based on shape.
  • Leaf arrangement is mainly limited to two basic petiole attachments and called either a simple leaf or a compound leaf. Compound leaves are further described as pinnately, palmately and doubly compound.

 

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Leaf Edges or Margins

Leaf Margin. 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".

Leaf margins can be finely classified as having a dozen or more unique characteristics. Here are four of the major classifications you need to know and into which all others will fit.

  • An entire leaf's margin is even and smooth around the entire leaf edge.
  • A toothed or serrated leaf's margin has a series of toothlike pointed teeth around the entire leaf edge.
  • A lobed leaf is an indention or indentions around the leaf edge that go less than halfway to the leaf midrib or midline.
  • A parted leaf is an indention or indentions around the leaf edge that go more than halfway to the leaf midrib or midline.
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Leaf Veins and Venation Patterns

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 as seen in the image.

Tree leaf veins in dicots (we also call these trees hardwoods or deciduous trees) are all considered to be net-veined or reticulate-veined or leaves with veins that branch from the main rib and then sub-branch into finer veins.

Here are the two classifications you need to know for tree identification:

  • Pinnate venation is when the veins extend from the midrib to the leaf margin. (oak, cherry)
  • Palmate venation is when veins radiate fan-shaped from the leaf petiole. (maple, sweetgum)
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Nix, Steve. "ID a Tree Using Leaf Shape, Margin and Venation." ThoughtCo, Apr. 23, 2017, thoughtco.com/id-trees-using-leaf-shape-venation-1343511. Nix, Steve. (2017, April 23). ID a Tree Using Leaf Shape, Margin and Venation. Retrieved from https://www.thoughtco.com/id-trees-using-leaf-shape-venation-1343511 Nix, Steve. "ID a Tree Using Leaf Shape, Margin and Venation." ThoughtCo. https://www.thoughtco.com/id-trees-using-leaf-shape-venation-1343511 (accessed May 24, 2018).