Dichotomous Keys PDF

Scientists use various tools to help them study and compare organisms. One of these tools is known as a dichotomous key. Dichotomous keys provide scientists with a way to identify an organism based on questions about opposing characteristics. If you were using a key about birds, a question might ask...

Scientists use various tools to help them study and compare organisms. One of these tools is known as a dichotomous key. Dichotomous keys provide scientists with a way to identify an organism based on questions about opposing characteristics. If you were using a key about birds, a question might ask if the bird’s beak is pointed or rounded on the end. Your answer would lead you to another question about the bird. You would continue to answer questions until you successfully identified the bird. Luckily, these tools are so easy to use, we can use them, too! Often, the hardest part about using a dichotomous key is understanding the terminology in the key. For example, most dichotomous keys dealing with plants use the following terms: leaf shape, veins, leaf margin, and arrangement. Leaf shape may describe the geometric shape the leaf most closely resembles or whether the leaf has lobes. Many keys also provide vein options such as pinnate (meaning veins grow away from a central vein in a uniform fashion) and palmate (meaning the veins start from a central point near the bottom of the leaf and spread out sporadically in various directions). The leaf margin is the outer edge of the leaf; this surface can be entire (meaning it is smooth with no wavy or pointed edges) or it can be toothed (with small points along the surface). Leaf arrangement is determined by how the leaves are arranged on a stem; simple leaves have only one leaf attached, while compound leaves have multiple leaflets attached. If we look at the dichotomous key, 1a. Compound leaf go to 2 left, we can use 1b. Simple leaf go to 3 the terms to 2a. Leaflets are palmate Buckeye determine which 2b. Leaflets are pinnate Locust leaf belongs to which tree. Let’s 3a. Veins are pinnate go to 4 3b. Veins are palmate go to 5 identify Leaf A. Starting with 4a. Leaf edge is toothed Birch question 1, we 4b. Leaf edge is entire Magnolia must first establish 5a. Leaf is star-shaped Sweet Gum if this is a 5b. Leaf is heart-shaped Redbud compound or simple leaf. Since there is only one leaf attached, we classify this as a simple leaf and move on to question 3. For question 3, we look at the veins. This leaf has pinnate veins because there is a central vein from which other veins come, leading us to question 4. If we study the edge of the leaf, we see it is jagged or toothed, telling us that this leaf belongs to a birch tree. See if you can use the dichotomous key to identify the other five leaves! Dichotomous Key for Leaves © Kesler Science, 2020