Within these groups, further subdivisions might take into account whether the leaves are composed of single blades, or are divided into leaflets. According to both the above criteria. A field guide to wildflowers might first group their species according to flower color, then within each of these groups, according to plant family. You'll just have to decide which approach is more appealing to you, and choose your guides accordingly. In general, beginners tend to prefer field guides based mostly on obvious physical traits, but experienced field workers find they can work faster and with greater accuracy using guides based on taxonomic relationships.
Field guides reveal much more about the items they cover than merely their names.
Special quirks of behavior are mentioned, such as constantly bobbing the tail up and down, which is what a Spotted Sandpiper does. This kind of information can be critical when identifying birds in the field. Even more useful are range maps. Let's say that you're in Chicago and a chickadee comes to your feeder. You know that several species of chickadee exist, and they all look pretty much alike.