Monocots vs. Dicots

Difference Between Monocots And Dicots

Botanists divide the flowering plants into two broad groups, or classes: the dicotyledons, or dicots, and the monocotyledons, or monocots. The dicots are by far the larger of the two, with more than 175,000 known species. Examples include most common garden plants, shrubs, trees, and broad-leaved flowering plants from magnolias to hollyhocks. Monocots number about 65,000. They include all grasses, as well as palm trees, lilies, orchids, and irises.

These two great classes have far more similarities than differences. But their evolution clearly diverged early in the history of the flowering plants. All dicotyledons, for example, begin life with two cotyledons, or seed leaves, hence their name (di-, meaning “two,” cotyledons). Similarly, all monocots begin life with a single (“mono”) cotyledon. The two groups have several other basic differences, which makes them easy to tell apart.

Half of all dicots are woody, which means that their stems expand in diameter with secondary growth. All flowering trees, for example, are dicots. Most monocots, by contrast, do not produce wood. Their stems remain herbaceous, or green. A few monocots, such as palm trees and bamboos, do produce a kind of pithy wood, not as organized or sturdy as that of dicot trees.

Monocots and dicots can likewise be distinguished by their leaves. The leaf of a typical monocot has parallel veins running its length. A grass blade and a palm frond clearly illustrate this pattern. In contrast, the leaf veins in dicots tend to form a broad, intricate net, or mesh, like that seen in a maple or oak leaf.

Looking through a microscope at the leaf of a monocot, one can see that its stomata (leaf pores), like its veins, lie in neatly parallel rows. In contrast, the stomata on the surface of a dicot leaf are usually scattered, with no clear organization readily perceptible.

These two groups can also be distinguished by their flowers. Most often, monocots produce blossoms whose parts (sepals, petals, and stamens) come in multiples of three, seldom four, but never five. This can be seen best in the blossom of a lily, and also in the tiny blooms of rice and other grasses. Most dicots have flower parts in sets of fours or fives. The examples are endless, from cactus blooms to roses.

Most monocots form masses of fibrous roots, where no one root is larger or more important than the others. The matted roots of crabgrass are a good example. By contrast, many dicots produce taproots, as seen in dandelions and root vegetables such as parsnips, carrots, and radishes.

A more fundamental difference between the two groups can be seen in a cross section of their stems. In monocots, the vascular tissue (water- and food-conducting cells) lies in bundles scattered throughout the stem. In dicots, the vascular tissue is organized in a distinct ring around the stem’s central core.

So far as they can tell, botanists believe that dicots are the older of the two groups. The first monocots probably evolved from a dicot well over 100 million years ago. Thereafter the two groups evolved separately.



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