A field guide is useful for identifying plants, but it's useless without knowledge of the words used for separating plants into groups.
Definite identification is only possible when a plant is in flower. Field guides arrange plants by their flowers. Many guides, such as A Field Guide to Wildflowers from the Peterson’s Field Guide series, organize the flowers by color. Newcomb’s Wildflower Guide groups plants by the number of regular parts to the flower; i.e., how many petals or petal-like parts the flower contains. There are separate categories for irregular flowers, which do not have petals arranged in a wheel pattern, or indistinguishable flowers, which are too small to make out the numbers or positions of the petals.
Newcomb’s has a binomial key in the front of the book that lists plants in such a way that the user may compare two descriptions of a feature, determine which category the subject plant falls into, and continue to the next pair of descriptions, until reaching a page that shows drawings of a small number of plants that are similar to the subject plant. By comparing the plant to the drawings and associated description, it is usually possible to identify any plant in flower found in the wild.
The first criterion in the Newcomb’s key is the number of flower parts, as described above. The second is the arrangement of leaves. Opposite leaves grows in pairs on opposite sides of the stem. Alternate leaves occur first on one side of the stem, with the next one down on the other side of the stem, and so on, alternating sides. Whorled leaves have more than two occurring at the same level, in a wheel pattern around the stem. Basal leaves emerge straight from the ground in a basal rosette or circular shape. Also at this level, wildflowers are distinguished from shrubs, which have multiple woody stems, and from vines, with long, weak stems that either creep along the ground or twine around other plants and objects. Trees are not included. (For information on identifying trees, see Opposite Tree Identification and Identifying Features of Trees.)
The next step is to determine whether the leaves are entire (with smooth edges), toothed or lobed (with jagged edges or smooth bulges), or divided (with indentations that go almost or all the way to the midrib of the leaf, sometimes producing separate leaflets, as with clover leaves).
From this point, the key offers a variety of criteria for comparison, which may include the size and color of the flower, the shape of the leaves, the arrangement of the flowers, the presence of spines or thorns, or other aspects of the plant’s structure. The number of comparisons varies according to the size of the group: there are far more plants with five-petalled flowers than with three, for example. It can be a thrill to discover the identity of an unknown flower--and the start of an intimate friendship.
