An inflorescence is a collection of flowers in a particular branching pattern that does not contain full-size leaves among the flowers. While there are many kinds of inflorescences to be found in flowering plants (angiosperms), each species has its own form of inflorescence, which varies only minimally in individual plants. However, if a plant bears only a single flower, or makes many single flowers scattered on a tree with interspersed leaves, no inflorescences are said to be present.
Inflorescences (sometimes called flower stalks) can be divided into two main categories, with many types within each. These two categories are determinate and indeterminate, and can be distinguished by the order in which the flowers mature and open. Determinate inflorescences mature from the top down (or the inside out, depending on the overall shape of the inflorescence). In other words, the oldest and therefore largest flowers (or flower buds) on a determinate inflorescence are located at the top (or center) while the youngest flowers can be found at the bottom (or outside edge). Thus, the flowers mature from the top down (or the inside out). The situation is reversed for indeterminate inflorescences: the youngest flowers are at the top and the oldest flowers are found at the bottom. Flowers in an indeterminate inflorescence mature from the bottom up (or the outside in). The terms determinate and indeterminate refer to the potential number of flowers produced by each inflorescence. In a determinate inflorescence, the number of flowers produced is determined by the manner in which the inflorescence is put together. An indeterminate inflorescence can continue to produce more flowers at its tip if conditions are favorable and are thus more flexible in flower number.
Each of the two broad categories of inflorescences can be divided into specific types. For the indeterminate inflorescences, the simplest types are the spike, raceme, umbel, panicle, and head. The spike has a single un-branched stem with the flowers attached directly to the stem. A raceme is similar, but the flowers each have their own short stems, which are attached to the main stem. An umbel has flowers with stems that all attach out in the same point on the main stem, resulting in an umbrella-like appearance that can be flat-topped or rounded. Panicles are highly branched with small individual flowers. A head typically has very small individual flowers that are collected in a densely arranged structure; sunflowers and daisies are good examples. Determinate inflorescences tend to be more branched and include the cyme, dichasium, and corymb. A cyme is a branched inflorescence where all flower pedicels and branches originate at the same point. A dichasium is more elongated and a corymb is flat-topped. All of these basic types can be further modified in shape and/or reiterated, resulting in complex inflorescences that can be very difficult to identify.
Inflorescences serve as a way for a plant to maximize its reproductive success. Flowers are collected into showy structures to better attract pollinators, to increase seed production, or aid in seed dispersal. Inflorescences can result in platforms suitable for insects or birds to land upon. Some inflorescences are tough and protect the floral parts from damage from the elements or from pollinating mammals.
see also Anatomy of Plants; Flowers.
Elizabeth M. Harris
Gifford, Ernest M., and Adriance S. Foster. Morphology and Evolution of Vascular Plants, 3rd ed. New York: W. H. Freeman and Company, 1989.
Harris, James G., and Melinda W. Harris. Plant Identification Terminology; An Illustrated Guide. Spring Lake, UT: Spring Lake Publishing, 1994.
Heywood, V. H., ed. Flowering Plants of the World. Englewood Cliffs, NJ: Prentice-Hall, Inc., 1985.
in·flo·res·cence / ˌinflôˈresəns; -flə-/ • n. Bot. the complete flowerhead of a plant including stems, stalks, bracts, and flowers. ∎ the arrangement of the flowers on a plant. ∎ the process of flowering.