What is a weed? Ralph Waldo Emerson declared a weed is "a plant whose virtues have not been discovered." But ask a gardener, farmer or weed control specialist, and the answers will range from "a plant of little value" to "a troublesome pest that affects the health of livestock and humans." A weed might best be defined as any plant growing where it is not wanted. Within each category they are further divided by color: blue, green, orange, pink, purple, white and yellow. Book has good diagrams and color pictures of leaf types. It is an excellent source of lesser- and well-known plants.

The key to mature plants has five categories:
1. Plants without leaves or with leaves reduced to small scales.
2. Plants with alternate leaf arrangement.
3. Plants with basal leaf arrangements.
4. Plants with opposite leaf arrangement.
5. Plants with whorled leaf arrangements

The key to seedlings has 9 categories of leaf arrangements.

The key to grasses has 3 categories of leaf base and inflorescence.