The characteristics of a leaf

Do you ever wonder what type of leaf is on your favorite tree? Have you noticed how many different types of leaf shapes there are? There are hundreds of different sizes, shapes and types of leaves. Too many for me to remember, even with my horticulture and landscape training, so this hub will be about some of the traits of leaves.

Firstly, there is the arrangement of leaves. This is how leaves are placed on the stem, such as opposite (leaves across from each other), alternate (leaves spaced at alternating spaces), subopposite (leaves generally across from each other, but not exactly), and whorled (3 or more leaves and buds growing from the same node). Take a walk in your neighborhood and try to figure out which trees show these leaf arrangements.

Secondly, leaves are either simple or compound. A simple leaf has a single bud in the axil and has a single leaf and stem. A compound leaf has a bud in the axil of a stem with more than one leaf. Compound leaves include, pinnately compound, palmately compound, odd pinnate, even pinnate, and bipinnately compound. Simple leaves can be seen on trees like Prunus emarginata (Bitter Cherry), and Acer rubrum (Red Maple). The compound leaf can be seen on Acer griseum (Paperbark Maple) and Aesculus hippocastanum (Common Horsechestnut). Collect some leaves on your walk and practice identifying them.

Thirdly, leaves have veins. Just like humans, but they don't carry blood, of course. They carry minerals, water and other elements taken from the soil. These are the tiny lines you see on leaves. The types of venation are, pinnate (veins extend from a central midrib), palmate (several main veins extend from the base of the leaf), dichotomous (the veins come from the base of the leaf and split forming a "y", found in Ginkgo leaves), and parallel (veins are parallel to leaf length). Look closely, with a magnifying glass, at leaf specimens you have collected and determine what the venation is.

Fourthly, don't forget the shape of a leaf. There are many types of leaf shapes and they can be confusing to identify. If you want to learn more about how to identify plants, I would suggest looking at Michael A. Dirr's, "Manual of Woody Landscape Plants." This volume contains almost everything you need to start identifying plants and is a great resource. Most of the information in this article comes from Dirr's book.

Leaf shapes vary from ovate, cordate (heart shaped), elliptical, spatulate (like a spatula), obovate, obcordate (reversed heart), linear, peltate (like a circle), and reniform (kind of like an umbrella). I listed just a few, but if you browse a good plant identification book you can find more.

Fifthly and lastly, leaves are also identified by their leaf base, margins and apices (tip). The leaf bases range from acute, rounded, cordate (heart shaped), truncate (straight), oblique (diagonal) and hastate (like an upside down "y"). Leaf margins include entire (smooth), serrate (jagged edge), serrulate, double serrate, dentate (a regular jagged edge), crenate (slightly jagged edge), undulate (wavy) and lobed (dissected, like a maple leaf). Apices are described by the point or lack thereof on the leaf tip as follows, acuminate (pointed), acute, obtuse (not a sharp point), truncate (no point), emarginate (indented tip), obcordate, mucronate (a small point) and cuspidate (bigger than mucronate). See what apices and bases the leaves you collect have.

Now that you know a little bit about leaf parts you could include certain plants as artistic additions to your garden, and knowing the leaf types will help you choose interesting and attractive plants for your yard. Learning or in my case, relearning, about leaf shape, margins, arrangement, bases and apices is interesting because I get to discover the beauty of plants all over again. I, also enjoy learning the latin names of plants and their anatomy. If you're interested in learning more about botanical names, I will be addressing the crazy world of plant nomenclature in another hub.

Dirr, Michael A. Manual of Woody Landscape Plants. Illinois: Stipes Publishing Company, 1990. Print