Inflorescence

Inflorescence is the arrangement of flowers on a plant, comprising the flowering axis (the peduncle), any branches and pedicels, and the flowers themselves. The pattern of inflorescence affects pollination opportunities, fruit development, and resource allocation, and it is a key feature used in plant identification and taxonomy. Inflorescences can be simple or highly branched and may be conspicuously visible or inconspicuous.

Inflorescences are commonly described as indeterminate (racemose) or determinate (cyme). In indeterminate inflorescences, the main axis continues to grow and flowers form from the apical region, so the oldest flowers are produced toward the base while the apex remains active. In determinate inflorescences, the terminal flower develops first and the axis terminates in a flower, with subsequent flowers produced below it.

Racemose (indeterminate) types include raceme, spike, panicle, and umbrella-like umbels. A raceme has flowers on short stalks (pedicels) along a central axis, such as in Delphinium or Convalaria. A spike features sessile flowers directly on the axis, as seen in certain grasses. A panicle is a branched raceme, common in many shrubs and herbs. An umbel gathers all pedicels from a single point, as in carrot or dill.

Cymose (determinate) types include the cyme and its derivatives, such as the corymb and helicoid cyme. In a cyme, the first flower develops at the apex and subsequent flowers arise below it; a corymb forms a relatively flat-topped cluster by varying pedicel lengths, while a helicoid cyme curves in a spiral as flowers mature.

Special forms include the capitulum (head) typical of Asteraceae, where numerous flowers form a compact disk, and the spadix-spathe arrangement found in Araceae. Catkins are slender, often pendulous inflorescences common in wind-pollinated trees such as willows and poplars.