Thursday, February 12, 2015

Winter Tree ID basics

Woody plants for the most part refers to trees and shrubs, and even though woody plants are dormant this time of year, they can still be identified. While most people find winter tree ID to be difficult, there are several characteristics that make it possible.
The first thing to notice is the leaf arrangement along the stem, which can be alternate, opposite, or whorled. “But it’s winter and there are no leaves!” you might exclaim. Well, there are clues you can look at to determine this. The process by which a tree sheds its leaves is termed abscission, which is a word that comes from Latin and means “to cut away.” When a leaf detaches from the branch, a scar remains visible at the point of attachment.
Observe the leaf scars on the twig in the photo. They are arranged in pairs or “opposite” from each other. This makes identification easy because there are not many woody plants that have opposite leaves and you can remember them with this simple mnemonic device: MAD Cap Buck Horse.
“MAD” stands for maple, ash, and dogwood. All species of maples (Acer spp.), ashes (Fraxinus spp.), and dogwoods (Cornus spp.) have opposite leaves, except for the appropriately named alternate-leaved dogwood (Cornus alternifolia). “Cap” stand for Caprifoliaceae, which is the honeysuckle family. All species in this family have opposite leaves and in Illinois the woody species include honeysuckle (Diervilla spp. and Lonicera spp.), elderberry (Sambucus spp.), coralberry (Symphoricarpos spp.), and different species in the genus Viburnum. “Buck” stands for buckeye (Aesculus spp.) and “Horse” stands for Horse Chestnut (Aesculus hippocastanum). There are very few possible exceptions, and most of these only look opposite (but are really whorled). Despite the exceptions, the vast majority of the time a woody plant with opposite leaves will be one of these options. The twig in this photo is Horse Chestnut, a non-native species that has been commonly planted in the US.
Also present in this photo, on the surface of the leaf scars, are bundle scars. This marks the severed connection of the vascular bundles that transport food and water between the twig and the leaf. This species has seven distinct bundle scars arranged in a U-shaped pattern. In fact, the bundle scar is shaped like a horseshoe, which may be where it gets its name.
Other features visible along the twig are dots called lenticels. Lenticels are present on some species and they are small openings that allow for gas exchange between the twig and the atmosphere. Near the left end of the twig in the photo is a group of rings that are called bud scale scars. This indicates the end of the previous season’s growth. You can actually determine the age of young trees by looking at the bud scale scars.
Lastly are the buds. Horse Chestnut has very large and resinous buds. Buds at the end of the branch are called terminal buds and buds that emerge from the side of the twig are called lateral buds. This marks the end of the current season’s growth and is where new twig growth will start from during the next growing season.
Opposite leaves, seven bundle scars, broad leaf scars at least ¼ inch across, with large (up to one inch) sticky buds keys out to Horse Chestnut.
Now that wasn’t that hard was it?

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