Is a Seed Plant a Dicot or Monocot?
- Cotyledons, or seed leaves, differ from true leaves in that cotyledons are present inside the ungerminated seed as part of the embryonic plant. True leaves only appear after germination. In most plants, cotyledons make up a large portion of the plant embryo. They play differing roles depending on the species of plant in question, but all cotyledons serve in some way to help the young plant make or access food during the first days after germination.
- For most dicots, cotyledons function very much like true leaves. They do not usually resemble the true leaves the plant later grows, however. For example, the cotyledons of a bean plant start off looking like the two halves of the original bean. The cotyledons grow thinner as the plant uses the nutrients they hold. The cotyledons also become green with exposure to light and start to photosynthesize, making even more food for the young plant. Taxonomically, all dicots belong to the class Magnoliopsida.
- In monocots, cotyledons do not always function as leaves. In fact, many monocots keep their cotyledons below the surface of the soil. However, below-ground cotyledons still help to supply the young plant with nutrients. Monocot seeds typically contain a food-storage structure, known as the endosperm, and the cotyledon acts as the conduit between the endosperm and the growing plant. Taxonomically, monocots belong to the class Liliopsida.
- Several aspects of plant structure and appearance align with the distinction between monocots and dicots. For example, flower parts such as petals and stamens usually come in multiples of four or five in dicots but in multiples of three for monocots. In dicots, leaves usually possess branching, networklike veins, such as on a rose leaf. Monocots have parallel, nonbranching veins, as on a blade of grass. Additionally, dicots tend to have a central root, or taproot, while monocots have fibrous roots that originate from a central point.
- The distinction between monocot and dicot only pertains to seed-bearing plants that also bear flowers -- the so-called angiosperms. Gymnosperms, such as pine trees, are also spermatophytes, but they do not flower. Gymnosperm seeds also contain cotyledons, but the number is more variable. For example, some gymnosperms have only two cotyledons, while others, such as the pinyon pine, have 12. For this reason, gymnosperms are often termed polycotyledonous plants.
