What are Cotyledons, Monocots and Dicots?

You can pot up your tomato seedlings when they have true leaves.
The true leaves look like small tomato leaves. The first 2 leaves were actually cotyledons. © Marie Iannotti

When's the last time you and your gardening friends were quibbling over whether a plant had 2 cotyledons or 1? Probably never. For something so straightforward, gardening is full of confusing terms, obscure Latin names, and contradictory terms. Cotyledon, a monocot, and dicot are not contradictory, but they sure are a mouthful. Although you won't see them used very often, they are useful terms to know when you are trying to key out or identify a plant.

Or trying to impress a garden snob friend.

What are Cotyledons?

Cotyledons are the first leaves produced by plants. Cotyledons are not considered "true leaves" and are sometimes referred to as "seed leaves" because they are actually part of the seed or embryo of the plant. The seed leaves serve to access the stored nutrients in the seed, feeding it until the true leaves develop and begin photosynthesizing.

In the photo at right, the two narrow leaves lowest on the stem are the cotyledons. The small, crinkled leaves on top are the first true leaves of this tomato seedling. The cotyledons will fall off as more true leaves develop. Most cotyledons look similarly nondescript, while the true leaves resemble the leaves of the mature plant.

What are Monocots and Dicots?

Flowering plants were divided into 2 classes: Monocotyledones (monocots) and Dicotyledones (dicots). As the names imply, the main distinction is the number of cotyledons present in the seed embryo - 1 or 2.

There are several other differences, such as the ones listed in the table below.



Petals in multiples of 3

Petals in multiples of 4 or 5

Stamens in multiples of 3

Stamens in multiples of 4 or 5

Parallel leaf veins

Branching leaf veins

Fibrous roots



Herbaceous or woody

Examples of Both Monocots and Dicots

What Does this Matter to the Gardener?

It's one of those things that pops up occasionally in garden books and leaves you scratching your head or feeling a little less knowledgeable. It shouldn't. While it's nice to know, it doesn't really make a difference in how you grow or care for plants. It's not even all that accurate a way of dividing plants.

Although the idea behind these classifications is to help in identifying plants, there is disagreement over the validity of dividing plants into these two classes. Some of the other traits used to classify can overlap. For example, there are exceptions in the number of flower parts, the arrangement of leaf veins, the vascular tissue in the stem, pollen structure, and root development. That's for the botanists to argue out.  For gardeners, it's just good to be aware that you may still find plants classified in this way.

Wait, there's More

Not all plants have cotyledons, which means they are neither monocots or dicots.

Plants that for spores, such as ferns, and plants that form cones, as with most evergreens, do not produce cotyledons. However, all plants that flower can be divided into either monocots or dicots.