The Tallgrass Prairie in Illinois

Prairie Plant Terminology — Inflorescences (Flower clusters)

An inflorescence is the group or arrangement in which flowers are borne on a plant. There are several parts to an inflorescence. The stalk of a whole inflorescence is the peduncle. The axis of the inflorescence is the rachis. The stalk of an individual flower is the pedicel. Sometimes bracts are found below the whole inflorescence or below each individual flower.

There are several basic types of inflorescences.

• simple cyme — an 3-flowered inflorescence in which the largest and oldest flower in in the center with two younger flowers on either side and below.
• compound cyme — a cyme with lateral branches. Inflorescences that are basically cymes occur commonly in plants, yet most cymes are modified in some way, usually with some or all lateral branches missing.
• raceme — an inflorescence in which a main axis produces a series of flowers on lateral stalks, the oldest at the base and the youngest at the top.
• spike — an unbranched inflorescence in which the flowers are without pedicels, that is the flowers are sessile and the youngest flowers are at the tip. Spikes can be thought of as racemes with sessile flowers.
• panicle — a compound raceme in which the flowers are borne on branches along the main axis or on further branches of these.
• corymb — a flat-topped inflorescence in which the pedicels of the lower flowers are longer than those of the flowers above, bringing all flowers to about the same level.
• simple umbel — an inflorescence in which all the individual flower pedicels arise in a cluster at the top of the peduncle and are of about equal length.
• comound umbel — instead of individual flowers radiating out from a single point, there are instead inflorescence branches. At the ends of each branch are secondary umbels.
• head — an inflorescence with sessile flowers aggregated into a dense cluster like the head of a pin. Characteristic of the aster or sunflower family (Asteraceae).

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