
A flower 'head' (''Bidens torta'') showing the individual florets
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 plant, in which single or multiple flowers develop on the same
stem. There are two fundamental terms used to describe the nature of inflorescences:
Determinate - the first flowers of the inflorescence to open are at the top end of inflorescence or terminal. The top flower blooms first.
Indeterminate - the first flowers to bloom are the ones at or near the bottom of the inflorescence, that is the first flowers start blooming at the bottom of the stem or inside a cluster of flowers.
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'' or ''
pseudanthium''. 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.
Some specialized terms used for inflorescences include:
★ Ament - a deciduous, spike like structure with scaly bracts that is unisexual and the flowers do not have petals.
★ Compound - a collection of two or more simple inflorescences aggregated together. e.g., panicle.
★ Catkin - a soft spike or raceme, composed of small unisexual flowers. After flowering is finished the structure (catkin) normally falls away as one unit. Birch tree.
★ Scorpioid cyme - a cyme which unfolds like a coil, the way a scorpions tall unfolds from under its body. Forget-me-not.
★ Solitary - with only one flower in the inflorescence. Many Tulips, Trillium.
★ Thyrse - compact, densely packed inflorescence that has an indeterminate main axis but is laterally determinate.
★ Verticil - the flowers are arranged in clusters around the nodes in whorls. Many plants in the
mint family.
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'.