Carpel evolution: Conduplicate, involute, appendicular and recepticular concepts, specialized carpels, poly and syncarpy, semi-inferior and inferior ovary. Evolution and types of placentation

Carpel evolution:- 

i. Conduplicate theory:- According to the most widely accepted hypothesis, the carpel constitutes a modified, conduplicate megasporophyll bearing two, adaxial rows of ovules (Figure 6.9D). Recall that a “megasporophyll” is a modified leaf that bears megasporangia, which in the seed plants are components of the ovules and seeds;

ii. Appendicular theory:- This theory was put forwarded by De Candolle, Van Teighem and others and

supported by Eames (1961). According to this theory the inferior ovary has developed as a result of

the fusion of the bases of sepals, petals and stamens and as such appended to the axis of the flower

which has nothing to do with the formation of the ovary wall. Eames stated that due to evolution,

inferior ovary was developed from the superior one by the process of gradual fusion of the bases of

sepals, petals and stamens and adnation of the same to the gynoecium wall which indicate the

superiority of inferior vary over inferior ovary.

iii. Receptacular theory:- According to Schleiden and others, the receptacle of the flower has become

the instrumental in the formation of the inferior condition of the ovary. This has achieved through the

gradual sinking of the ovary to the deep cup shaped receptacle with the process of invagination of the

tip of the thalamus. After sinking down of the ovary the bases of sepals, petals and stamens have been

fused much in the same manner as in case of the appendicular theory.

Specialized carpels:- The most specialized carpels are uniovulate and indehiscent and occur acyclically in great numbers in each flower, with strong trends toward monoecism and even dioecism.

Polycarpous and Syncarpous Ovary:-

i. Apocarpous Ovary:-

Separation:- In apocarpous ovaries, the carpels remain separate from each other, forming individual pistils.

Multiple Ovaries:- Each carpel in an apocarpous ovary has its own distinct ovary.

Varied Arrangement:- The carpels may be arranged in a spiral or whorl pattern, resulting in a diverse floral structure.

Genetic Variation:- The separate pistils in an apocarpous ovary allow for potential variation in seed development and fruit formation.

Examples:- Buttercups and strawberries are examples of plants that exhibit apocarpous ovaries.

ii. Syncarpous Ovary:-

Fusion:- In syncarpous ovaries, the carpels are fused together to form a single pistil.

Shared Ovary:- The fused carpels result in a common ovary that is shared among the carpels.

Coordinated Development:- The fused carpels work together for efficient reproduction and coordinated development of seeds.

Floral Symmetry:- Syncarpous ovaries often contribute to radial symmetry in flowers, creating a balanced and aesthetically pleasing structure.

Examples:- Roses and lilies are examples of plants that possess syncarpous ovaries.

Classification of Ovary:- On the basis of position, the ovary can be classified into three types:

i. Superior Ovary:- When the ovary is attached to the receptacle of the flower, above the other floral whorls, it is known as the superior ovary. Such ovaries are found in fleshy fruits such as berries and drupes. The flower that has a superior ovary is termed as hypogynous. Examples: pea, beans.

ii. Half-inferior Ovary:- When the ovary is embedded and surrounded by receptacles in the flower, it is known as half-inferior ovary. The flowers with half-inferior ovaries are called perigynous. This type of ovary can be seen in the family of Lythraceae in plants such as crape myrtles. In this type, the ovary is half above and half below the insertion point.

iii. Inferior Ovary:- When the ovary is present below the attachment point of other floral parts on the flower, it is called an inferior ovary. This type of ovary can be seen in pome fruits. The flowers which have an inferior ovary are termed as epigynous. Examples: orchids, Fuschia

Evolution and types of placentation:-

Placentation:- It is defined as the arrangement of ovules within the ovary. several different forms of placentation can be seen in flowering plants.

Types of Placentation:-

i. Marginal:- The ovules develop in rows near the margin on the placenta formed along the ventral suture. It occurs in monocarpellary and unilocular ovary, E.g., Leguminosae.

ii. Parietal:- The placenta is formed by the swelling up of cohering margins, and on the latter develop the ovules in rows. It occurs in bicarpellary or multicarpellary but unilocular ovary, E.g., Papaveraceae.

iii. Axile:- Here, the placentae develop from the central axis which correspond to the confluent margins of carpels. It occurs in bi-to multilocular ovary, E.g., Solanaceae, Malvaceae.

iv. Free-central:- Here, the placenta develop in the centre of the ovary as a prolongation of floral axis and the ovules are attached on this axis. It occurs in multicarpellary but unilocular ovary, E.g., Primulaceae.

v. Superficial or Laminar:- Here, the ovules develop over the entire inner surface of the carpels. It occurs in multicarpellary ovary, E.g., Nymphaea.

vi. Basal:- The placenta develops directly on the thalamus and bears a single ovule at the base of the unilocular ovary, E.g., Compositae.