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How Can I Tell a True Leaf From a Cotyledon?

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Cotyledons are the first leaves to emerge from the soil when a plant germinates. Because they are part of the seed’s embryo, they also are known as seed leaves, and provide nutrients to the seedling until its true leaves unfurl and begin the process of photosynthesis. Plants with only one cotyledon or seed leaf are called monocots, but most plants have two, making them dicots. Those leaves usually are easy to pick out, as they look nothing like the plant’s true ones.

Down and Dirty Cotyledons

Seed leaves usually are smooth and plain looking, with a very basic shape. For dicots, they appear directly opposite each other on the stem. Because they are the first leaves a plant makes, they always will be the lowest ones, and won’t look like the adult foliage of the plant. A seedling sheds its cotyledons eventually, sometimes within a few days of sprouting, sometimes up to a year later. If the plant has hypogeal germination, as with peas, the seed leaves remain below the soil and you probably won’t see them at all, except possibly during transplanting. On monocots, such as grasses and lilies, the single seed leaves also frequently are hidden.

High and Handsome True Leaves

The true leaves unfurl above the cotyledons on the seedling, and look like a smaller version of the plant’s adult foliage. They are more decoratively shaped than seed leaves and often hairier, and all of the later leaves will match them in appearance.

Telling the True From the Temporary

It usually is easy to tell which leaves are the cotyledons. As they are the first the seedling produces, they will be the lowest ones on the stem, the ones to which an empty seed case often clings. They also won’t look like any of the other leaves on the plant.

To Pinch or Not to Pinch

Some people like to pinch off the cotyledons after the true leaves emerge. Unless those leaves are in the way, however, it is best to allow the seedling to decide when it is done with them, or you may accidentally break its stem instead. You may need to snip off the cotyledons when you are dividing annual vegetables, which like to be transplanted more deeply than they grew in the seedling flat. Those include tomatoes (Lycopersicon esculentum) and members of the cabbage family (Brassica spp.), for which you should remove the seed leaves and plant the seedlings so that their first true leaves are just above the ground.

References
  • University of Florida IFAS Extension: Seedling Images
  • Penn State Extension: Seed and Seedling Biology
  • University of Rhode Island: Session Three — Germinating Seeds
  • Green Harvest: How to Raise Seeds Successfully
  • The Plant Book; Susan Page and Margaret Olds
Photo Credits
  • Comstock Images/Stockbyte/Getty Images
About the Author

A former master gardener with a Bachelor of Arts in writing from Houghton College, Audrey Stallsmith has had three gardening-related mysteries published by WaterBrook Press, a division of Random House. Her articles or photos have also appeared in such publications as Birds & Blooms, Horticulture and Backwoods Home.

How Can I Tell a True Leaf From a Cotyledon?. Cotyledons are the first leaves to emerge from the soil when a plant germinates. Because they are part of the seed’s embryo, they also are known as seed leaves, and provide nutrients to the seedling until its true leaves unfurl and begin the process of photosynthesis. …

What Are Cotyledons, Monocots, and Dicots?

Helen Lawson/Getty Images

For something so straightforward, gardening is full of confusing terms, obscure Latin names, and contradictory terms. Although you won’t see them used often, they are useful terms to know when you are trying to key out or identify a plant.

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 provided, the two narrow leaves lowest on the stem are the cotyledons. The small, crinkled leaves on top are the first true leaves of this 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.

Monocots and Dicots

Flowering plants are divided into two 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:

Monocot

Dicot

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

Herbaceous or woody

Examples of Both Monocots and Dicots

  • Monocots include most of the bulbing plants and grains, such as agapanthus, asparagus, bamboo, bananas, corn, daffodils, garlic, ginger, grass, lilies, onions, orchids, rice, sugarcane, tulips, and wheat.
  • Dicots include many of the most popularly grown garden flowers and vegetables, including legumes, the cabbage family, and the aster family, such as apples, beans, broccoli, carrots, cauliflower, cosmos, daisies, peaches, peppers, potatoes, roses, sweet pea, and tomatoes.

Is Classification Important?

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, but 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.

Not All Plants Follow the Rules

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

Plants are classified as monocots or dicots, based on traits like the number of cotyledons, or seed leaves, they develop in their embryo. ]]>