What Is a Cotyledon?
A cotyledon is the first leaf or one of the first pair of leaves to develop in the embryo of a seed plant. Often referred to as a "seed leaf," its primary role is to provide stored food and nutrients to the young plant during germination before it can produce its own food through photosynthesis.
Section 2: Function and Types
The main function of a cotyledon is nourishment. In some plants, like beans and peas, the cotyledons are thick and fleshy because they have absorbed the food reserves from the seed's endosperm. In other plants, like corn, the cotyledon is thin and helps transfer nutrients from the endosperm to the embryo. Plants are broadly classified based on the number of cotyledons they possess: monocotyledons (monocots) have one cotyledon, while dicotyledons (dicots) have two.
Section 3: A Practical Example
A common bean is an excellent example of a dicot. If you split a soaked bean seed, you will see two large halves; these are the cotyledons. When the bean sprouts, these two fleshy seed leaves emerge from the soil and provide energy for the initial growth of the stem and true leaves. In contrast, a corn kernel (a monocot) has only one cotyledon, which remains underground and transfers food from the endosperm to the growing shoot.
Section 4: Importance in Plant Classification
The number of cotyledons is a fundamental characteristic used to classify flowering plants (angiosperms). This distinction between monocots and dicots is linked to other features. For instance, dicots typically have net-like veins in their leaves and flower parts in multiples of four or five, while monocots usually have parallel veins and flower parts in multiples of three. Understanding cotyledons is therefore crucial for identifying and classifying plants.