Understanding Cotyledons and Their Role in Plant Growth: The Powerhouse of the Seed

Cotyledons may be one of the first visible signs a plant has germinated, but what is a cotyledon? It is the embryonic part of a seed which stores fuel for further growth.

Seeds are the earliest part of the plant life cycle and cotyledons are seed leaves which fall off a plant within a few days of sprouting. There are cotyledons on plants that grow above the soil and photosynthetic. They take in the light and feed the plant so it can grow. There are also hypogeal cotyledons which remain under the soil but serve the same purpose.

These unique plant parts are a crucial step of plant emergence after germination. Cotyledons help the new plant store energy to grow. Let's dig in and explore more.

Types of Cotyledons

You can study hypogeal cotyledons by viewing a split peanut. The cotyledon is the two halves of the peanut we eat as a snack! Photosynthetic cotyledons are those first little leaves that appear when seedlings sprout and will look quite dissimilar from the true leaves of the plant. They eventually fall off when the true leaves come in.

Scientists use the number of cotyledons to classify plants. A monocot has only one cotyledon and a eudicot has two. Corn is a monocot and has an endosperm, embryo, and single cotyledon. Beans can be easily split in half and each side will bear a cotyledon, endosperm, and embryo. Both forms are considered flowering plants, but the blooms are not always evident.

Monocot vs. Eudicot Seed Leaves

The number of cotyledons in a seed is the basis for classifying any plant in the angiosperm or flowering plant group. There are a few fuzzy exceptions where a plant cannot simply be designated monocot or eudicot simply by its number of cotyledons, but these are rare. Magnolia trees are ancient and an example of this oddity.

When a eudicot emerges from the soil, it has two seed leaves whereas a monocot will bear only one. Most monocot leaves are long and narrow while dicots come in a wide range of sizes and shapes. Flowers and seed pods of monocots tend to come in parts of three while dicots have three or five petals and seed heads come in a host of forms.

Trillium, orchids, tulips, lilies, daffodils, and irises are examples of flowering monocots. Corn, wheat, sugarcane, and bamboo are agricultural monocots.

Roses, daisies, petunias, pansies, geraniums, and sunflowers are examples of flowering eudicots. Apple trees, tomatoes, beans, peas, and mint are other eudicots you may grow.

When Do Cotyledons Fall Off?

Photosynthetic cotyledons remain on the plant until the first true leaves appear and can begin to perform photosynthesis. This is generally just a few days and then the seed leaves fall off. They remain to help direct the energy stored in the seed to new growth, but once the plant is self-sufficient, they are no longer needed.

Similarly, the hypogeal cotyledons that remain under soil are also directing stored energy from the seed and will wither when no longer needed. Some plants’ cotyledons persist for up to a week, but most are gone by the time the first two true leaves are evident.

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