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Botany for Gardeners: Taxonomy – Classes of Flowering Plants, Monocots and Dicots

Aster_alpinus blueThe plants that dominate the world today are known as flowering plants because of their method of reproduction. They produce ovules (flower eggs) that are completely contained within the ovary and the pollen has to penetrate the ovary into to fertilize the ovules. The ovary is contained within the flower that may have large showy petals like a rose, or lack petals like a peperomia, a popular houseplant grown for its foliage. Petals are only one part of a flower and the presence of an unseen ovary, not petals, put a plant in the division known as “Flowering Plants”, or Angiosperms (meaning “enclosed seeds”).

Flowering plants developed into two distinct groups known as classes; monocots and dicots. The second syllable of these words, “cot” refers to a structure known as a cotyledon or seed leaf. A cotyledon is a storage organ in the seed. It comes out comes out of the soil when the seed germinates and gradually shrinks as stored food is transferred to the growing seedling. Flowering plants have either one or two cotyledons. Monocots have one cotyledon and dicots have two cotyledons. Orchids, lilies, grasses, palms, bamboo, and irises are examples of monocots while roses, maple trees, and sunflowers are examples of dicots. Dicots are the most common flowering plants with over 200,000 species world-wide. Monocots are represented by 50,000 species world-wide and more of both monocots and dicots may yet to be found.

There are some obvious differences between monocots and dicots and a quick look at a plant will usually enable you to distinguish them. Monots leaves have parallel veins while dicots have netted veins.

Parallel (iris)

Parallel (Monocot)

Black eyed Susan

Net (Dicot)

Flower parts of monocots come in 3’s while those in dicots are in 4’s and 5’s.

Parts in 3's (Monocot)

Parts in 3's (Monocot)

Parts in 5s (Dicot)

Parts in 5's (Dicot)

After examining flowers and leaves if you are still unsure of the class, you can look at the branching and root system. Monocots have simple branching while dicots usually have complex branching. Monocots also have horizontal rootstalks, while dicots usually have a tap root.

Here’s the same information in a chart form.

Number of seed leavesOneTwo
Veins patternParallel Net
Flower parts3’s4’s, 5’s
BranchingSimple; symmetricalComplex; asymmetrical
Root systemHorizontalTaproot
ExamplesGrass, iris, palmRose, sunflower, maple

There are exceptions to every rule but most of the time an examination of the leaf and flower will lead to the correct classification. Sometimes, however, a very close examination is necessary; for example, the leaves of plantain appear to have parallel venation but actually have a fine network of veins between the larger veins. There are other morphological differences between monocots and dicots but special equipment is needed to discern them.

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Recommended Reading:

From Seed to Plant
Trees: Their Natural History
Oh Say Can You Seed?