Seeds play a vital role in plant reproduction. They are the end result of sexual reproduction in plants, a characteristic specific to angiosperms and gymnosperms. Gymnosperms, which lack fruits or flowers, have exposed or “naked” seeds. In contrast, angiosperms have matured ovules that turn into fruits following fertilisation.

Angiosperms can be categorised as either monocots or dicots, based on the number of cotyledons in the seed. A seed is made up of an embryo encased in a protective outer layer known as the seed coat. Some seeds are known to have a triploid endosperm. An embryo is comprised of three parts: a radicle, an embryo axis, and cotyledons.

Angiosperm seeds are classified into two types based on the number of cotyledons:

1. Monocotyledonous seeds
2. Dicotyledonous seeds

Read on to learn more about dicotyledonous and monocotyledonous seeds.

Structure of a Dicotyledonous Seed

• Beans, walnuts, and pistachios are examples of dicotyledonous or dicot seeds.
• Dicotyledons, also known as dicots, are a group into which all the flowering plants or angiosperms were previously classified. The term dicotyledons is derived from the presence of two embryonic cotyledons in the seed. To date, about 200,000 species of dicotyledons have been discovered.
• In a dicotyledonous seed, the embryo consists of an embryo axis and two cotyledons. The cotyledons often appear swollen because they act as a food reserve for the developing seedling. The embryo axis has two ends. The upper part that forms the shoot tip is called the plumule, while the lower part that forms the root tip is called the radicle. The entire content is encased within a protective cover known as the seed coat. The seed coat consists of an outer layer called the testa and an inner layer called the tegmen. Additionally, the seed is attached to the fruit through a structure known as the hilum.
• Other examples of dicot seeds include oranges, cherries, and apricots.

Structure of a Monocotyledonous Seed

• Oats, barley, and millet are examples of monocot seeds or monocotyledons.
• Embryos of a monocotyledonous seed have only one large cotyledon called the scutellum. The scutellum, typically shield-shaped, is located laterally towards one side of the embryo axis. Like in dicotyledons, the embryo axis of monocotyledons has a shoot tip, plumule, enclosed in a sheath called the coleoptile, and a root tip, radicle, enclosed in the coleorhiza. In a monocotyledonous seed, the endosperm is covered by a proteinous layer known as the aleurone layer.
• Most monocotyledonous seeds are albuminous seeds, which means they have a thick, swollen endosperm for nourishment. The endosperm is not entirely consumed during embryo development, and it serves as the nourishing tissues in seeds. However, some monocots like orchids are exceptions.
• Other examples of monocot seeds include turmeric, pineapple, maize, leeks, and palm.