A flower is a modified condensed shoot specialized to carry out sexual reproduction in higher plants. Like a branch, it arises in the axil of a small leaf-like structure called bract. The terminal part of the axis of a flower, which supports all the floral appendages (i.e.,sepals, petals, stamens and carpels) is called receptacle (thalamus or torus). The receptacle consists of several crowded nodes which are separated by condensed internodes. The internode of the branch that lies below the receptacle is called pedicel. A bract is usually situated at the base of pedicel. Sometimes small leaf-like structures are present in the middle of pedicel. They are calledbracteoles.
The concept that the flower is a modified or a metamorphosed shoot for the purpose of reproduction is an old one and the concept is gradually developed through the past and is accepted at the present by a majority of morphologists. Linnaeus expressed this idea in his Philosophia Botanica (1751) by the phrase 'vegetative metamorphosis' . This concept that floral leaves were a modification of vegetative leaves was further elaborated by Caspar Wolff and Decandolle.
The 'foliar theory' of the flower of the earlier botanists is held today by many though modified in one form or other by other botanists.
That the flower is a modified shoot, is only a figurative expression, and implies that the floral leaves are vegetative leaves and transformed to do a different function of reproduction, in the place of the ordinary function of photosynthesis.
The position of flower buds and shoot buds is same, i.e., they are terminal or axillary in position.
In some plants, the flower buds are modified into vegetative buds or bulbils, eg. Agave, Onion, etc.
In some plants, the thalamus elongates to form a vegetative branch or another flower above the first flower, e.g. Rose.
In Nymphaea (Water Lily), the flowers show all transitional stages between a sepal and petal and between a petal and stamen.
In Gynandropsis gynandra, the thalamus elongates and shows long internodes between the floral organs.
In rose, the sepals are similar in morphology to leaves.
In Degeneria, the stamens are expanded like leaves and the carpels appear like folded leaves without differentiating into stigma and style.
Anatomy of the thalamus, pedicel and stem show close similarities. The vascular supply of different floral appendages resemble the vascular supply of ordinary vegetative leaves.
A flower is usually seen either at the axil of a leaf or at the apices of the stem and its branches. Accordingly, the flower is described as axillary and terminal respectively.
Flower, whether solitary or in inflorescence, usually has a short stalk called pedicel. A flower with stalk is described as pedicelleteand a flower without stalk is called sessile.