Inflorescence: Definition, Biology & Types

Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

Flowers are arranged in a variety of ways on different plants, and there are specific names for each type of arrangement. Learn more about the different flower clusters in this lesson.

The Science of Flower Arrangements

Have you ever walked through a field and seen a variety of plants and wildflowers? Did you notice how the flowers were arranged differently on the stems of each plant? Each unique arrangement has its own name and description. In plant biology, we call the grouping or cluster of flowers on a branch or a network of branches an inflorescence.

We can categorize the type of inflorescence based on how the flowers are arranged on the main stem that supports the inflorescence, which is called the peduncle, and the timing of flowering. The simplest classification includes two groups: determinate inflorescence and indeterminate inflorescence.

Inflorescence Descriptions

Determinate Inflorescence

In a determinate inflorescence, the oldest flower is located in the middle of the cluster, at the end of the main axis, and the peripheral, younger flowers grow from axillary buds.

  • A cyme is a flat-topped determinate inflorescence where the flowers in the middle open first and are followed by the surrounding, younger flowers, which grow around the peduncle.
  • A scorpioid cyme is a specific type of cyme inflorescence where the flowers only grow on one side of the peduncle.

In a cyme inflorescence the oldest flower is in the middle, and the younger flowers surround it to the sides
cyme inflorescence

Indeterminate Inflorescence

In an indeterminate florescence, the peduncle continues to produce new flowers, so the older flowers are found around the outside of the cluster, and the youngest flower is in the middle. There are several types of indeterminate florescence.

In a raceme, a single flower grows on its own short stalk, called a pedicel, at an upward angle between the peduncle and the branch of a leaf. In this arrangement, multiple flowers grow along a long, unbranched axis.

In a raceme inflorescence, single flowers shoot out from the main stem on short stalks called pedicels
Raceme inflorescence

A panicle is like a branched raceme, and each branch has more than one flower on it.

A spike is an arrangement similar to a raceme, except the flowers grow directly from the stem and are not on pedicels. A 'catkin' is a specialized type of spike in which the flowers are either all males or all females.

A catkin willow salix where flowers grow directly off the stem

A corymb is a raceme where the pedicels of the lower flowers are longer than the pedicels of the upper flowers. This arrangement give the cluster a flat-topped appearance, with the youngest flowers in the center.

A corymb inflorescence has a flat top appearance
corymb inflorescence

An umbel is an arrangement where each pedicel originates from approximately the same point at the top of the peduncle; thus, the flower cluster has an umbrella-like appearance. hemlock-parsley and wild carrot have this inflorescence.

A spadix is a spike on top of a fleshy stem. The largest unbranched inflorescence in the world belongs to the corpse flower which sports a spadix. This spadix also happens to smell just like rotting flesh to attract beetles and flies which serve to pollinate it.

A spadix inflorescence is a spike on a fleshy stem, shown here with a Flamingo lily
spadix inflorescence

A head is a short, dense spike with flowers growing directly on the peduncle, which is flat and broad. Thus, the inflorescence appears to look like a single flower.

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