Inflorescence
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An inflorescence is a group or cluster of flowers on a branch of a plant. In botany, the term refers to the way individual flowers are arranged on the axis (floral stem). An inflorescence is said to be indeterminate if the number of flowers may increase after the first flower opens, even while others are opening, and determinate if the number of flowers cannot increase after the first flower opens. With indeterminate inflorescent clusters, the most proximal flowers (ie. those closest to the base) open first; in the case of determinate flower clusters, the most distal flowers (ie. those furthest from the stem) open first.
There are numerous kinds of inflorescences, some characteristic of families or orders of plants. Following is a list of terms used to describe inflorescences with links to examples:
- A corymb is a racemose (see raceme) inflorescence that is flat-topped or convex because the outer pedicels are progressively longer than the inner ones (see also umbel).
- A cyme is a class of determinate inflorescences characterized by the terminal flower blooming first.
- A head is a dense, indeterminate inflorescence of [sessile] or subsessile flowers crowded on a compound receptacle; sometimes called a capitulum. Characteristic of the Asteraceae.
- A panicle is a branched, indeterminate inflorescence with pedicellate (having short floral stalks) flowers on the secondary branches.
- A raceme is an unbranched, indeterminate inflorescence with pedicellate (having short floral stalks) flowers along the axis. Compare with spike.
- A spadix is a stalk with flowers densely arranged around it, enclosed or accompanied by a spathe. It is characteristic of the Araceae.
- A spike is an unbranched, indeterminate inflorescence with sessile flowers arranged along the axis. Compare with raceme.
- An umbel is a type of raceme with a short axis and multiple floral pedicels of equal length that appear to arise from a common point. Inflorescence characteristic of the Apiaceae. A compressed cyme is called umbelliform if it resembles an umbel.
In some plants, especially those in family Proteaceae, the inflorescence may be a complex structure consisting of many smaller inflorescences. For example, Banksia flowers occur in pairs, which are then clustered together to form a dense head. In such cases, the term "inflorescence" may be ambiguous. To deal with this, it has been proposed that a cluster of inflorescences be termed a "conflorescence" or "synflorescence". This terminology has been in use for around 30 years, but has not been widely adopted.
In some plants, the structure that holds the flowers together persists until fruit is formed, resulting in a fruiting structure in which individual fruit are embedded. In such cases, the fruiting stage of the inflorescence is termed an infructescence.
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