An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified. The modifications can involve the length and the nature of the internodes and the phyllotaxis, as well as variations in the proportions, compressions, swellings, adnations, connations and reduction of main and secondary axes.
The stem holding the whole inflorescence is called a peduncle and the main stem holding the flowers or more branches within the inflorescence is called the rachis. The stalk of each single flower is called a pedicel.
The fruiting stage of an inflorescence is known as an infructescence.
A flower that is not part of an inflorescence is called a solitary flower and its stalk is also referred to as a peduncle.
Source : http://en.wikipedia.org/wiki/Inflorescence
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