"The sweet pea has some of its leaflets changed to tendrils which hold it to the trellis. Its flower is like that of the clover, the upper petal forming the banner, the two side petals the wings, and the two united lower petals the keel which protects the stamens and pistil."
-Anna Comstock, Handbook of Nature Study, page 589
We learned about the family in our botany studies, which is characterized by its irregularly shaped flower containing five petals: a banner, two wings and a keel (which is comprised of two petals that look like one).
The Pea Family also produces pea-like pods that open along two seams and often have pinnate (opposite) leaves. We don't have any peas growing in the garden and we have never been able to find any blooming members of the family in our neighborhood except the clover. I have invited the boys, in the past, to find clover in the backyard and to bring some inside to sketch, and when they did, they found White Clover.
The clover's petals are hard to identify as a banner-wings-keel because they are so long and thin, but looking at the clover closely, they noticed that the flower is made up of many small flowers, each with their own calyx. Several years ago, Katie examined some clover thoroughly and was able to draw the flower as it looks from far away and then a cut-out that shows the flower pattern.
"The white clover has creeping stems. Its flowers depend upon the bees for their pollination and the bees depend upon the white clover blossoms for honey." Handbook of Nature Study, p.597
Sam noticed several years ago, when we studied white clover, that the bees were swarming the clover one day but not so much the next. We had learned the previous year, when we studied bees, that bees choose a different flower each day to get the nectar from, so this made sense.
They also noticed that the flowers are not all just white. The leaves, too, are not just a single green, but several shades and some even had hues of red in them. Other members of the Pea Family include lupine, most beans and legumes and alfalfa.
Those are the basic ways to determine the difference between Monocots and Dicots. There are other ways to tell them apart, such as pollen structure and root development.
Why is it helpful to know the differences between them? Again, it is easier to look a plant up if you can determine which category it falls in. Plant Field Guides are written by botanists, so it is helpful to be able to think like a botanist, if you want to find things in Field Guides.