Exercises - Basic inflorescence terminology

E x t e n s i on G a r d e n e r - B o t a n y E x e r c i s e s

Introduction Defense Twigs and buds Leaf structure Leaf shape Flower structure Inflorescence type

Basic inflorescence structure

This exercise focuses on basic inflorescence terminology. The term inflorescence is used to describe the arrangement of flowers on a plant. There are a number of patterns of floral display, from simple axillary flowers to complex, compound displays, that are repeated throughout the plant tree of life. The stalk of an inflorescence is called the peduncle, whereas the stalks of the individual flowers in the inflorescence are called pedicels. However, when flowers are borne in a solitary fashion (i.e., not in a multi-flower inflorescence), the flower stalk is also called the peduncle.

For the following exercise, first study the images below to review the terms used to describe the basic types. For a definition of each type, mouse-over the image. Then, carefully study the unsorted images at left and drop each thumbnail into an appropriately labeled box on the right. Clicking on a thumbnail will expand the image. Click submit to check yourself. To reset, click clear or just refresh your browser.

In the illustrations below, each circle represents a flower. Larger circles represent older flowers.

Indeterminate inflorescences

Raceme: An unbranched, elongated inflorescence with pedicellate flowers, maturing from the bottom upwards (Harris & Harris 1994)

Raceme: An unbranched, elongated inflorescence with pedicellate flowers, maturing from the bottom upwards (Harris & Harris 1994)

Spike: an unbranched, elongated inflorescence with sessile or subsessile flowers or spikelets maturing from the bottom upwards (Harris & Harris 1994)

Catkin: a lax spike or raceme of apetalous, unisexual flowers (common in Betulaceae and Fagaceae; Harris & Harris 1994).

Flat Umbel: a highly condensed raceme, in this case flat-topped, with the pedicels arising more or less from a common point (Harris & Harris 1994).

Round Umbel: a highly condensed raceme, in this case convex, with the pedicels arising more or less from a common point (Harris & Harris 1994).

Compound Umbel: an umbel of umbels (each a highly condensed raceme with the pedicels arising more or less from a common point; Harris & Harris 1994).

Simple Corymb: a flat-topped or round-topped inflorescence, racemose, but with the lower pedicels longer than the upper (Harris & Harris 1994).

Compound Corymb: a corymb of corymbs (each a flat-topped or round-topped inflorescence, racemose, but with the lower pedicels longer than the upper; Harris & Harris 1994).

Head: a dense cluster of sessile or subsessile flowers (Harris & Harris 1994); common in Asteraceae and Rubiaceae.

Determinate inflorescences

Solitary: Occurring singly, not in a cluster or group (Harris & Harris 1994)

Cyme: a flat-topped or round-topped, determinate inflorescence, in which the terminal flower blooms first (Harris & Harris 1994).

Helicoid Cyme: a one-sided cymose inflorescence coiled like a spiral or helix (Harris & Harris 1994); common in Boraginaceae.