Dichotomous Keys

Master dichotomous keys! Identify plants & animals with our science worksheet. Fun, step-by-step classification practice.

What is a dichotomous key? Dichotomous keys are used to identify a variety of things including insects, plants, animals and rocks. A key gives pairs of “either-or” choices that direct the user to the next pair of choices (also known as a couplet) or to the point of identification. Dichotomous keys are also used for identifying and classifying new species. Sometimes dichotomous keys use technical terminology which can make it difficult for users who lack experience in the field.Adichotomous keybegins with broad-ranged questions or statements which get more specific. For example, the first question in a dichotomous key about birds might ask if the bird can fly or if it is flightless. Questions further down in the key get more specific and may ask about the size of the bird, the shape of the beak, the color of the feathers, etc.Dichotomous Key Usage Example – Shade Trees in Tampa BayBelow are the first 6 of 9 couplets in a dichotomous key to identify 1 of 10 different shade trees found in Tampa Bay, Florida. With stems and leaves from the tree, the user starts at the couplet 1a and 1b and determines if the leaves and buds are opposite or alternate. If they are opposite, the user goes to couplet 2, if they are alternate, they go to couplet 3. The user then works their way through the couplets until they identify the tree species.Notice that based on couplet 1a and 1b, if the leaf and bud orientation is opposite (Go to 2), the tree is either a Florida maple or a red maple depending on whether the leaf margins are entire or serrated. If the leaves and buds are alternate (Go to 3), the user must go into more detail using the key to identify the tree. In this case, the subsequent couplets go into more detail about the morphology of the leaves. Use the dichotomous key below to label the smiley faces. 1. Teeth visible ....................go to 2.....Teeth not visible .................go to 42. Has a wide, toothy smile .......Smilus toothyus....Is not smiling ......................go to 33. Visibly crying .................Smilus dramaticus.... Frowning .......................Smilus upsettus4. Eyes are symmetrical .... go to 5....Eyes not symmetrical .....go to 85. Eyes shaped like hearts .....Smilus valentinus....Eyes are shaped as ovals .....go to 66. Smiling, happy face ......Smilus traditionalis.....Not happy, frowning or other .....go to 77. Mouth curved down, frowning ....Smilus saddus.... Mouth is a small circle .................Smilus suprisus8. Has a pirate eye patch ...............Smilus piratus....Does not have eye patch ............ go to 99. One eye is much larger than the other eye .....Smilus mutatusOne eye is winking .................Smilus winkus Label the smiley faces according to the Dichotomous Key above.Suppose you discovered the new smiley like the one at the very bottom: What name would you give it? Be sure to label the alien. Smilus dramaticus Smilus saddus Smilus winkus Smilus upsettus Smilus mutatus Smilus traditionalis Smilus piratus Smilus valentinus Smilus suprisus Smilus toothyus Students were asked to identify the following birds using the classification key shown. Bird 1 is a Ruby-throated hummingbird and Bird 2 is a Tufted titmouse. Bird 2 is a Great blue heron and Bird 3 is an Ovenbird. Bird 2 is a Red-tailed hawk and Bird 3 is a Killdeer. Bird 1 is an Ovenbird and Bird 3 is a Tufted titmouse. The key shown can be used to classify different kinds of plants.Looking at the key, which of these plants is a gymnosperm? A scientist sees the organism shown in an aquarium and uses a key to help classify the species. Based on the key, what species did the scientist observe? spotted moray eel spotted eagle ray glassy sweeper glasseye snapper A scientist observes the following organism and uses the key to help classify the organism.Based on the key, what type of organism did the scientist collect? bird shellfish insect sea jelly Some students collected leaf samples. The students used the leaf dichotomous key shown below to identify a leaf sample.Based on the dichotomous key, which type of tree is this sample from? Ginkgo Horse Chestnut Honey Locust Black Maple Trish constructed a dichotomous key to help identify the reptiles and amphibians living in a certain area.Which phrase describes a lizard? An animal with scaly skin and a shell but no external gills An animal with scaly skin and legs but no shell An animal with legs and costal grooves but no tail An animal with external gills and a tail but no costal grooves Did you like or dislike this lesson? Explain your selection.