In angiosperms, the flower is the reproductive part of the plant. The typical structure of the flower consists of four whorls arranged successively on the stalk or pedicel termed as thalamus or receptacle. The four whorls are namely, calyx, corolla, androecium and gynoecium.
The calyx and corolla are accessory organs. In some plants, they are not distinct parts, hence together they are known as perianth.
The androecium consisting stamen is the male reproductive organ and gynoecium consisting of carpels is the female reproductive organ. However, in some plants, the flower is bisexual. The presence of stamen or carpel alone in the flower is known as unisexual.
The symmetry of the flower: If the flower can be divided into two equal radial halves by passing any radial plane, then the flower is said to be actinomorphic (E.g. mustard). When the flower is symmetrical by passing one vertical plane, then it is said to be zygomorphic (E.g pea). The flower could be asymmetric in shape if it cannot be divided into similar halves by passing any plane (E.g Canna).
Floral appendages: Based on the number of floral appendages, the flower may be trimerous, tetramerous or pentamerous. Presence of a reduced leaf at the base of the flower, bracts are called as bracteate and absence of bracts is called ebracteate
Based on the position of the flower on thalamus: Depending on the position of calyx, corolla, and androecium with respect to the ovary on thalamus, the flowers can be divided into three types namely, hypogynous, perigynous and epigynous
Hypogynous: In this type, the gynoecium is present at the highest position with other parts present beneath it. Hence, the ovary of such flowers is said to be superior (E.g Mustard plant)
Perigynous: In this type, the gynoecium is situated in the center and other parts of the flower are present around the gynoecium at the same level. In this type of flowers, the ovary is said to be half-inferior (E.g rose)
Epigynous: In this type, the margin of thalamus grows upward, thus enclosing ovary completely. The other parts of the flower are present above the ovary, thus the ovary of these flowers is said to be inferior. (E.g cucumber)
A. Hypogynous B & C. Perigynous D. Epigynous
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