Unformatted text preview: Species Identification and Phylogenetic Inference Species Classification Background: A dichotomous key is a tool that allows the user to determine the identity of items in the natural world, such as trees, wildflowers, mammals, reptiles, rocks, and fish. Keys consist of a series of “either or” choices that lead the user to the correct name of a given item. A dichotomous key is a listing of characteristics, such as structure and behavior, organized in such a way that an organism can be identified or classified. Dichotomous means "divided into two parts". Therefore, dichotomous keys always give two choices in each step. For example, a question in a dichotomous key for trees might be something like, "Are the leaves flat or needle like?"