Flower is the reproductive part of the angiosperm which consists of four whorls i.e.
Calyx and Corolla are known as non-essential or accessory whorls because they are not involved in the reproduction. However, they provide beauty to the flower. Androecium and Gynoecium are known as essential or reproductive whorls because they are directly involved in the reproduction. Flowers with all these four whorls is known as a complete flower and that without any of these four whorls is known as an incomplete flower. Flower with both androecium and gynoecium is known as bisexual flower and that without one of these two whorls is known as a unisexual flower.
The small leafy pointed structure known as bract may be present at the base of the flower. Flower with bract is known as bracteate flower and without bract is known as an ebracteate flower. A whorl of bracts is known as involucre. Eg; Sunflower and sterile scaly bracts present at the base of spikelet that encloses flowers is called glume. Eg; Wheat. In some cases, a secondary bract arises at the base of individual flower known as bracteole. The flower with bracteole is called bracteolate.
The divisibility of the flower vertically in two halves is a symmetry of the flower. The symmetry of the flower may be actinomorphic, zygomorphic, asymmetrical(irregular).
Actinomorphic: If a flower can be divided into two equal longitudinal halves from more than one vertical planes passing through the centre then it is known as an actinomorphic flower. Eg; Brassica, Solanum.
Zygomorphic: If a flower can be divided into two equal longitudinal halves from only one vertical plane passing through the centre then it is known as a zygomorphic flower. Eg, Pisum, Lathyrus.
Asymmetrical: If a flower cannot be divided into two equal longitudinal halves from any vertical plane then it is known as an asymmetrical flower. Eg; Canna
The thalamus is the swollen tip of a pedicle or the floral axis on which the floral whorls are developed in a cyclic manner. On the basis of shape of thalamus angiospermic flower can be categorized into three types;
In this type, the thalamus is swollen at the topmost position of which lies the ovary and other floral parts arise below the ovary on the thalamus so that the position of ovary becomes superior and other floral parts become inferior. Example; Brassica, Solanum.
Here the thalamus is cup-shaped in which ovary lies at the central position and other floral parts arise around the ovary on the rim of the thalamus. Due to this, the position of ovary becomes semi-inferior and other floral parts superior in nature. Eg; Rose
Here the thalamus is cup-shaped with a deep cavity which encloses the ovary and other floral parts arise above the ovary on the thalamus so that the ovary becomes inferior and other floral parts superior in nature. Eg; Tagetes