Tree leaves come in a variety of shapes and forms. One of the most important areas of concern is the outside edge of the leaf, which can be classified be as either smooth, serrated, toothed, bristled or lobed. Sometimes serrated and toothed are regarded as one in the same, but once you determine that you have a truly toothed leaf, the list of possible trees has been greatly narrowed down.
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Evergreen or deciduous
Leafy trees (and conifers) can be separated into two basic groups depending on whether the leaves fall from the plant when the days become shorter or if they remain on the tree for the entire yearly cycle. These two conditions are respectively referred to as deciduous and evergreen. For the most part, toothed leaves grow on deciduous trees, but there are a few specimens of evergreens with a toothed edge.
Simple or compound
Another great dividing point between how leaves grow on a tree is how many leaflets grow beyond each point of attachment to the wood stem, called a petiole. A simple leaf has one leaf, while a compound leaf has many small leaflets attached together. With the compound leaf there is no swelling where the leaflets joins together, but you will find a swollen spot at the petiole base. This swelling is caused by the presence of a leaf bud, which grows into a complete leaf during the spring season.
Opposite or alternate
The way in which a leaf is attached to the stem also effects the classification. With trees, the single and alternate attachments are most common. Among trees found in the UK, only the dogwoods, maples, buckeyes and ashes have opposite attachment and among these four groups only the buckeye has toothed leaves.
Observing the overall shape of the leaf will help separate a birch from an elm and a cottonwood from a chestnut. Generally speaking, there are many types of leaf shapes, but when looking at toothed leaves, identifying these basic shapes will go a long ways toward identifying the tree. With an elliptical-shaped leaf, the apex and base of the leaf blade come to a point and middle section is much wider. This term describes leave such as the elm, chestnut and beech. Other leaves will have a wide base with a pointed tip. This kind of outline can be further divided into cordate (heart-shaped) and ovate (egg-shaped). Cordate leaves are wider at the base than ovate leaves. Finally, there are palmate leaves, which spread out like fingers on your hand.
Unfortunately for the dendrologist, there are many trees with single, alternate, deciduous and toothed leaves. At this point the distinction between these trees will need to be expanded to studying the flowers, fruit and seeds. A careful study of the fruit and seed will narrow down the options, especially when separating individual species of the same genus.
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