From Seed to Seed:
Plant Science for K-8 Educators

Angiosperms. Aside from the conifers, most of our common garden plants are classified as angiosperms, or flowering plants. Evolutionarily, this enormous group of plants represents the youngest and most highly developed group of plants. The term angiosperm is derived from the Greek words for "vessel" and "seed," alluding to the fact that their seeds develop within an ovary, a protective structure within the flower.

Angiosperms represent an advancement over gymnosperms not only in that their seeds are more protected, but also in their modes of pollination. Gymnosperms rely solely on wind to transfer pollen, whereas many of the angiosperms enlist the help of insects and other animals for transferring pollen and increasing the likelihood of fertilization.

Monocots and dicots. The angiosperms are divided into two groups: the monocots and the dicots. This distinction is based on the number of cotyledons, the food storage structures, in their seeds. Monocots have one cotyledon, dicots have two. As you have probably noticed throughout the course, we have also used the terms monocotyledons and dicotyledons to describe these plants.

A good example of a dicot is a bean plant. After the bean seeds have been soaked, students can divide them in half, lengthwise, into the two cotyledons. Inside are the embryonic stem, root, and tiny leaves. When the seed germinates, the two cotyledons emerge from the soil to form the seed leaves. The seed leaves nourish the plant until it can form its true leaves. (Not all dicots' seed leaves emerge during germination; for example, peas are dicots, but the pea cotyledons remain underground.)

Corn is an example of a monocot. Corn seed has one cotyledon and can't readily be split.

Familiar monocots include grass, corn, iris, palm, and lily. Monocots share other distinctive features: The veins in the leaves are usually parallel, flower parts (for example, petals) are often in threes or multiples of three, and, lacking a vascular cambium, they don't form wood in their branches and trunks.

Dicots, on the other hand, are characterized by branched or netlike veins in the leaves; their flower parts are commonly found in fours or fives, or multiples thereof. Many dicots do have a vascular cambium; these plants are able to produce secondary xylem, or wood. All of the woody trees and shrubs in your garden are dicots, as are many herbaceous plants such as tomato, squash, and zinnia.

Now that we have talked about these different types of plants, let's go out in the garden and have a look.