Inflorescence
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 determinate if the number of flowers cannot increase after the first flower opens; in determinate flower clusters, the most distal flowers (furthest from the stem) open first or all open at about the same time. If the number of flowers can increase even as some are opening, the inflorescence is said to be indeterminate. In indeterminate inflorescences, the most proximal flowers (the ones closest to the base) open first.
A flower head (Bidens torta) showing the individual florets
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 or raceme with a short axis and multiple floral pedicels that appear to arise from a common point. Inflorescence characteristic of the Apiaceae. A compressed cyme is called umbelliform if it resembles an umbel.