Inflorescence

Red clover inflorescence (spike)

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 inflorescenes, that is the first flowers start blooming at the bottom of the stem or inside a cluster of flowers.

A flower head (Bidens torta) showing the individual florets

Poinsettia inflorescence, showing several florets

A Banksia grandis inflorescence may have 6000 individual 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.
• Spike - the flowers are arranged on a single axis and have no pedicels(stems that hold flowers)The flowers are joined close to the stem in a long row.
• 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.