Carpels Or Gynoecium
• Carpels or female reproductive parts form the innermost whorl of a flower. The free occurring unit of gynoecium is called pistil, which consists of basal swollen ovary, a stalk like style and a terminal receptive part called stigma.
• Depending on the number of carpels, gynoecium may be monocarpellary, bicarpellary, tricarpellary, tetra- carpellary and pentacarpellary having one, two, three, four and many carpels respectively.
• Ovary has one or more chambers or loculi (singular loculus): unilocular (e.g., pea); bilocular (e.g., mustard); trilocular (e.g., Asparagus): tetralocular (e.g., Ocimum): pentalocular (e.g., China rose); multilocular (e.g., Althaea, lady’s finger).
• In the chambers are present oval outgrowths called ovules. Ovules later mature into seeds while the wall of the ovary forms a covering called pericarp. The two together constitute a fruit.
• A sterile and undeveloped pistil is called pistillode.
Stylopodium : When base of the style is swollen to form a pad like structure, it is called stylopodium, e.g., family Apiaceae (Umbelliferae).
Plumose stigma : Feather like stigma is called plumose stigma, e.g., grasses.
Resupination : Turning or twisting of ovary or flower through 180°, i.e., upside down is called resupination. e.g., most orchids.
Cohesion of carpels
Apocarpous : Gynoecium comprises of free carpels, e.g., Ranunculus.
Syncarpous : Gynoecium comprises of two or more carpels which are fused, e.g., Hibiscus.
Types of style
Terminal : Style lying in the same straight line with the ovary, e.g., Hibiscus.
Lateral : Style arising from the side of the ovary, e.g., Potentilla.
Gynobasic: Style arising from the depression in the centre of the ovary or directly from thalamus, e.g., Ocimum.
Placenta is a parenchymatous cushion present inside the ovary where ovules are borne. An ovary may have one or more placentae. The number, position, and arrangement or distribution of placentae inside an ovary is called placentation. It is of the following types.
Marginal placentation : Occurs in a monocarpellary, unilocular ovary. The placenta develops and ovules are borne along the junction of the two margins of the carpel, e.g., members of family Leguminosae.
Parietal : Occurs in a bi-or multicarpellary syncarpous ovary. There are two or more longitudinal placentae attached to the ovary wall. Ovary can be unilocular or become falsely two or more locular due to ingrowth of placentae or formation of false septum, called replum. e.g., members of family Brassicaceae.
Superficial : Occurs in multicarpellary, multilocular ovary. The ovules are borne on placentae which develop all around the inner surface of the partition wall, e.g., Nymphaea.
Axile placentation : It occurs In polycarpellary syncarpous gynoecium. The ovary is many chambered. The walls of the carpels in the centre of the ovary are u nited to form an axis, which bears the placentae with ovules, e.g., Petunia (bilocular), Asphodelus (trilocular), tomato (bi or tetralocular), Hibiscus (pentalocular), Althaea and lemon (multilocular).
Free central: The pistil is polycarpellary and syncarpous but the ovary is unilocular. The ovules are borne around a central column which is not connected with the ovary wall by any septum, e.g., Dianthus, Silene, Primula, etc.
Basal : The pistil can be monocarpellary or syncarpous. The ovary is unilocular. It bears a single placenta at the base with generally a single ovule, e.g., Ranunculus, Sunflower, Marigold.
• The thalamus is the swollen part of the flower which lies at the tip of the pedicel and bears floral organs.
• In some plants, thalamus shows distinct nodes and internodes. The internode between calyx and corolla is termed as anthophore, e.g., Silene; that between corolla and androecium, the androphore, e.g., Passiflora; and that between androecium and gynoecium, the gynophore or gynandrophore, e.g., Cleome.
• Sometimes thalamus is prolonged into gynoecium to form a central axis it is called carpophore, e.g., coriander.
Relative position of floral organs on thalamus
• There are three forms of thalamus as regards the insertion of pistil and androperianth (other floral organs) viz., hypogyny, epigyny and perigyny.