How to Identify Dicot and Monocot Seeds: Structure, Examples & Uses
Seeds are an essential element of sexual reproduction in plants. It is formed as the end product of sexual reproduction in plants and is exclusive only to angiosperms and gymnosperms.
Gymnosperms have no fruits or flowers; hence, their seeds are exposed or “naked”. On the contrary, angiosperms have matured ovules that develop within the fruits after fertilisation. It has an embryo which is covered in a protective outer covering called the seed coat. Some seeds have been documented having a triploid endosperm. An embryo is composed of three parts- a radicle, an embryo axis, and cotyledons. There are two types of monocotyledonous and dicotyledonous seeds depending on the number of cotyledons.
Structure of a Dicotyledonous Seed
Some of the examples of dicotyledons or dicot seeds are peas, almonds and cashews
Dicotyledons seeds are also called dicots as they belong from the group in which all the flowering plants or angiosperms were formerly divided. The name dicotyledons refer to the seed having two embryonic cotyledons and there are around 200,000 species of dicotyledons discovered till date.
In dicotyledons, the embryo has an embryo axis and two cotyledons. Cotyledons look swollen as it acts as a food reserve for the developing seedling. The embryo axis has two ends. The upper tip is named as plumule and therefore the lower end is called the radicle. The whole content is enclosed within a protective cover called the seed coat and the seed coat is made up of an outer layer that is called the Testa and an inner layer called Tegmen. Moreover, the seed is attached to the fruit through a structure that is called Hilum.
Other dicot seeds examples include apples, plums and peaches.
Structure of a Monocotyledonous Seed
Some of the examples of monocot seeds or monocotyledons are Corn, wheat and rice
Embryos of a monocotyledonous seed possess just one large cotyledon called scutellum. The scutellum is usually shield-shaped and is located laterally towards a side of the embryo axis. The embryo axis of monocotyledons consists of a shoot tip, plumule, enclosed inside a sheath called coleoptile and a root tip, radicle, enclosed in coleorhiza as in dicotyledons. In a monocotyledonous seed, the endosperm is covered by a proteinous layer called aleurone layer.
Almost all monocotyledonous seeds are albuminous seeds, i.e., they have thick, swollen endosperms for nourishment. The endosperm is not completely consumed during embryo development, and it is the nourishing tissues in seeds. However, some monocotyledons like orchids can be treated as exceptions.
Some other examples of monocot seeds are ginger, banana, sorghum, onion, coconut and garlic.
Seed Germination
Similar conditions are required for both the monocot and dicot seed germination. The seeds should be completely developed with an embryo, an endosperm and right numbers of cotyledons and a testa. In this process, cotyledons and endosperms support the growing plant as a food source until the photosynthesis begins. An optimal environmental condition will be required for seed germination.
Steps of Germination in Monocots and Dicots
Seed germination begins with a seed absorbing water, which results in the swelling and a softening of a seed’s coat or testa. The water initiates biochemical activity in the seed. Monocots have starchy seeds and require only 30 percent moisture content to germinate. Dicots have oily seeds and can begin germination after reaching a minimum of 50 percent of moisture content. After this, a lag phase gives the prospect for a seed to start the internal processes like the cell respiration, protein synthesis and metabolism of food stores. After this, cellular division and elongation occur, pushing out the seed’s root and radicle.
In monocots, the basis that emerges is roofed by a coleorhiza, or sheath. Its seedlings’ leaves then come forth, during a layer referred to as a coleoptile. A primary root emerges from the seed in dicots,. This root allows water absorption by the new plant as this is a radicle. An apical meristem will eventually develop from this radicle and produce the plant’s rootage. Then its shoot comes first from the seed, consisting of the cotyledons, hypocotyl and epicotyl. Seedlings grow slowly after they emerge above the soil in both monocots and dicots,.The seedling first develops its roots and then its true leaves which will photosynthesize and convert sunlight to energy for the plant.
FAQs on Dicotyledonous vs Monocotyledonous Seeds: A Complete Guide
1. What is a dicotyledonous seed?
A dicotyledonous seed, also known as a dicot seed, is produced by flowering plants and is distinguished by having two embryonic leaves, or cotyledons. These cotyledons often store the food reserves required to nourish the embryo during germination. A typical dicot seed consists of an outer protective layer called the seed coat and an inner embryo.
2. What is a monocotyledonous seed?
A monocotyledonous seed, or monocot seed, is a seed that contains only a single embryonic leaf or cotyledon. These seeds are characteristic of plants like grasses, maize, and rice. In many monocots, the main food storage tissue is the endosperm, and the single cotyledon (called a scutellum in grasses) helps in transferring these nutrients to the developing embryo.
3. What are the main differences between a dicotyledonous and a monocotyledonous seed?
The primary differences between dicot and monocot seeds are:
Number of Cotyledons: Dicot seeds possess two cotyledons, whereas monocot seeds have only one.
Endosperm: In most mature dicot seeds (like beans), the endosperm is absent as it is absorbed by the cotyledons. In monocot seeds (like maize), the endosperm persists and serves as the primary food source.
Embryo Structure: Monocot embryos have unique protective sheaths, the coleoptile (protecting the plumule) and coleorhiza (protecting the radicle), which are not found in dicot embryos.
4. What are some common examples of dicotyledonous seeds?
Common examples of dicotyledonous seeds include most legumes, pulses, and many common fruits. Specific examples are:
Pea (Pisum sativum)
Gram (Cicer arietinum)
Bean (Phaseolus vulgaris)
Mango (Mangifera indica)
Mustard (Brassica)
5. What are some common examples of monocotyledonous seeds?
Monocotyledonous seeds are characteristic of most cereals and grasses. Well-known examples include:
Maize (Zea mays)
Rice (Oryza sativa)
Wheat (Triticum aestivum)
Onion (Allium cepa)
Orchids
6. Why is the endosperm absent in mature dicot seeds like pea and bean?
In non-albuminous or exalbuminous dicot seeds like pea and bean, the endosperm is absent at maturity because it is completely consumed by the embryo during its development inside the ovule. The food reserves from the endosperm are relocated to and stored in the two large, fleshy cotyledons, which then provide nourishment during germination.
7. How do the cotyledons in a monocot seed (like maize) differ in function from those in a dicot seed (like a bean)?
In a dicot seed like a bean, the cotyledons function as the primary food storage organs. In contrast, the single cotyledon in a monocot seed like maize, known as the scutellum, does not store food. Its primary role is to secrete enzymes that digest the stored food in the separate endosperm and facilitate the transfer of nutrients to the growing embryo.
8. What is the importance of the coleoptile and coleorhiza in a monocot embryo?
The coleoptile and coleorhiza are crucial protective sheaths found only in monocot embryos. Their importance is:
The coleoptile is a pointed sheath that encloses the plumule (embryonic shoot). It protects the delicate shoot tip as it pushes through the soil.
The coleorhiza is a sheath that covers the radicle (embryonic root). It protects the emerging root tip from damage during germination.
9. What are the main parts of a typical dicot embryo?
A typical dicot embryo comprises an embryonal axis and two cotyledons. The part of the axis above the cotyledons is the epicotyl, ending in the plumule (future shoot). The part below the cotyledons is the hypocotyl, which terminates in the radicle (future root).
10. Can a plant be identified as a monocot or dicot without examining its seed?
Yes, a plant's classification can be determined by its overall morphology. Key indicators include:
Leaf Venation: Monocots exhibit parallel venation (veins run parallel), while dicots show reticulate venation (net-like pattern).
Root System: Monocots typically have a fibrous root system, whereas dicots usually have a prominent taproot system.
Flower Parts: In monocots, floral parts (like petals) are in multiples of three. In dicots, they are in multiples of four or five.
