GYNECIUM: CHARACTERISTICS, PARTS, TYPES, FUNCTIONS - BIOLOGY - 2025

The gynoecium is the female reproductive organ of the flower, composed of the set of carpels in phanerogamic plants. The carpel is the floral whorl specialized in the production of female gametes or ovules.

In this regard, carpels are a group of megasporophils or fertile leaves that carry longitudinally folded megasporangia. In the internal part it develops one or more macrosporangia or seminal primordia that will eventually give rise to the ovule.

Carpels of Paeonia officinalis (Peonia). Source: flickr.com

In gymnosperms the free and open carpels support the ovule without any specialized structure. In fact, they lack an ovarian cavity; without differentiation between styles and stigmas, the ovules are displayed without any protection.

In the case of angiosperms, the gynoecium is made up of a group of carpelar leaves that fuse in the form of a cavity. This structure, called the ovary, contains the seminal primordia where the ovules develop.

characteristics

Magnolia wieseneri gynecium. Taken and edited from: Peter coxhead, Wikiklaas.

The gynoecium is the fourth flower whorl and represents the female reproductive system of the flower. It is generally located in the central part of the flowers, and is surrounded by a group of reproductive units known as carpels or megasporophils.

The fusion by folding of the megasporophils allows the formation of a chamber called the pistil, which consists of the ovary, stigma and style. The ovary is the concavity where the ovules develop, the stigma receives the pollen, and the style allows the union between both structures.

The ovary is the basal part of the gynoecium, it is made up of the carpelar leaves and the ovules are inserted inside it. In this regard, carpels are modified leaves that cover the ovules or seminal primordia.

The ovoid-shaped ovules of just millimeters are born on the placenta on the inside of the carpels. In this case, the placenta, made up of highly vascular tissue, supports the ovules by a peduncle called a funiculus.

Pistil of the passion flower (Passiflora caerulea). Source: pixabay.com

The narrow, tubular shaped structure that allows the ovary and stigma to join is called the style. It is the area that the pollen tube runs through on its way from the stigma to the ovum.

Finally, the stigma responsible for collecting pollen is located through specialized structures such as absorbent hairs or sticky surfaces. The stigma presents the ideal conditions for the development of the pollen tube, and thus transport the male gametes from the pollen grain to the ovule.

Parts

-Stigma

It is a structure located in the upper part of a carpel, or of several united carpels. It is the part in charge of receiving the pollen grains, for which they have a sticky surface. It can be located directly on the ovary, or attached to it through style.

-Style

Tubular structure formed by the folding of a carpel or by the fusion of several carpels. It is in charge of joining the stigma with the ovule and its length can vary from very long to very short, and it may even be absent in some species.

-Ovary

It is the basal portion of a single carpel, or of several fused carpels, and it will contain one or more ovules. Pollination will take place inside the ovary and the fertilized ovules will transform into seeds. After pollination, the ovary will grow and transform, to become the fruit, or part of it.

According to its relative location, the ovary can be classified into three different types:

Super

The ovary is located above the flower receptacle, while the components of the remaining whorls join the receptacle below the ovary. Flowers that have ovaries in this location are called hypogynous (below the gynoecium).

Semi-inferior

Also called the middle ovary, this is located at the middle level; the perianth and / or the androecium are inserted at the middle of the length of the ovary, which is located in an intermediate position. Flowers with a semi-inferior ovary are called perigine (around the gynoecium).

Inferus

In this case, the ovary is located within the floral receptacle, while the perianth and / or the androecium are located in the upper part of the ovary. The flowers that have this type of ovaries are called epigines (above the gynoecium).

The ovaries can also be classified based on the number of carpels that constitute them, in that case we will have ovaries of the following type:

Unicarpel

The ovary is made up of a single carpel that folds back on itself to close. For example, beans, peas, and beans are single-skinned.

Bicarpel

In this case, two carpels fuse to give rise to a single ovary, for example in belladonna and potato.

Multilayer

Also called pluricarpel, similar to the previous case, the ovary is formed by fusion of carpels, but in this case more than two of them are involved. Malvaceae, in general, have this type of ovaries.

Finally, each ovary can have one or more ovules inside. In this case, the ovaries will be classified following an order similar to that indicated above, into uniovular, biovular or multiovular. Examples of each of these cases would be turkey tail, casuarina and beans, respectively.

Diagram of a mature flower. Taken and edited from LadyofHats.

Features

As mentioned before, the gynoecium is the female reproductive structure of flowering plants. Its function is related to the production of female sexual gametes, their protection, facilitating pollination, protecting the seeds once they are formed and in many cases, helping their dispersal.

Stigma

Its function is to receive the pollen grains for the fertilization of the ovules, and to facilitate this the stigma has an adherent surface for the pollen.

Style

It communicates the stigma with the ovary and its function is to allow the passage of the pollen tube. When the pollen grain adheres to the stigma, it germinates to produce a pollen tube, which will grow through the style until it reaches the ovary.

Ovary

The ovary will contain one or more ovules to be fertilized by pollen. When the pollen tube enters the ovary, it will produce sperm cells that will fertilize the eggs.

When fertilization occurs, the ovum will turn into a seed. Additionally, the pollen tube can produce other sperm cells that will fuse with two polar nuclei located in the center of the embryo sac, coming from the female gametophyte to form a structure called the endospermic nucleus or endosperm.

The endospermic nucleus has the peculiarity that it is triploid and its function is to divide by mitosis to produce food that will be used by the developing embryo. This process is called double fertilization and is characteristic of flowering plants.

After fertilization, the ovum will grow and develop to produce the fruit, or part of it. The main function of this fruit will be to help in the dispersal of the seeds to new areas. For this, the fruits can be fleshy and have a pleasant flavor to attract animals that will eat them and disperse the seed directly or through the feces.

In other cases, the fruits may have structures that allow them to adhere to the animals and thus facilitate the dispersal of the seeds, or they may also have structures that facilitate aerial dispersal.

Types of ovary

In botany, the ovaries are the structure of the gynoecium that forms the seminal cavity that contains the mature ovules for fertilization. The classifications are diverse based on the position, number of carpels or number of ovules that allows classifying the types of ovaries.

According to the position of the ovary, in relation to the different parts of the flower, the following classification is obtained:

• Supero: the ovary is located on the flower receptacle. The sepals, petals and stamens unite at the level of the receptacle. Flowers with an ovary of this type are called hypogynous.
• Middle or semi- inferior : the ovary is located in an intermediate position. The sepals, petals and stamens are inserted at the level of the hypanthus. The flowers are called perigine.
• Inferus: the ovary is located within the flower receptacle. The other flower whorls attach to the top of the ovary. Flowers with an ovary of this type are called epigines.

Based on the number of constitutive carpels, the ovaries can be classified into:

• Unicarpellate: the structure is formed by a single carpel. For example, in legumes.
• Bicarpellar: The structure has two carpels: For example, in the Solanaceae.
• Multilayer or multilayer: the structure is formed by three or more carpels. For example, Malvaceae.

Regarding the number of ovules present in each ovary, they can be classified into:

• Uniovular: ovaries that have a single ovum. For example, in asteraceae such as sunflower.
• Biovular: ovaries that have two ovules. For example, in Umbelliferae such as carrot.
• Multiovular or pluriovular: ovaries that have more than three ovules. For example, in fabaceae such as peas.

Ovaries in the flower. Source: Espaciociencia.com

Placentation

Placentation is related to the disposition of the seminal primordia that will give rise to the ovules on the ovary. That is, the position of the attachment points of the eggs on the placenta in the ovary.

The placenta is the inner tissue of the ovary where the foliar primordia join. The arrangement and number of placentas is subject to the number of carpels that constitute the ovary.

Placentation occurs in different forms, the most common being:

• Apical: it occurs when the placenta is located at the apex of a unilocular ovary.
• Axillary: in the case of gynoecium formed by more than two carpels, each one closes on itself, forming partitions. In this way, the placenta becomes embedded at the level of the armpits of the septa.
• Basal: when the column is compressed on the base of the ovary, the placenta is located in the basal area of ​​the unilocular ovary.
• Central: it occurs in that gynoecium that lacks partitions between the carpels, leaving only a central column. There the placenta is located in this central axis of the ovary.
• Marginal: it is observed when the ovules join the placenta at the marginal level, at the edges of the carpelar tissues.
• Parietal: it occurs when the gynoecium is made up of more than two carpels united across the edges. Thus, the ovules join the placenta at the level of the inner walls of the ovary.

References

1. Huaranca Acostupa Richard Javier (2010) The flower, inflorescence and fruit. National University of the Peruvian Amazon. Biological Sciences Faculty. Academic Department of Botany. 14 pp.
2. Megias Manuel, Molist Pilar & Pombal Manuel A. (2018) Plant Organs. Flower. Atlas of Plant and Animal Histology. Faculty of Biology. University of Vigo.
3. Menéndez Valderrey, JL (2018) El gineceo. Nº 381. ISSN 1887-5068. Recovered at: asturnatura.com
4. Flower Morphology (2010) Plant Morphology Course. National University of La Plata. Faculty of Agricultural and Forest Sciences. 14 pp.