Corymb

Flowers come in many shapes and sizes. When a flower cluster has a flat or dome-shaped profile, it is said to be corymb [kor-im].

Carrot umbel (Alvesgaspar) CC BY-SA 3.0

Corymb comes to us from the Greek word (korumbos) for ‘cluster’. The only reason this information is important, besides helping you win more often in word games, is that it can help you to identify plants of mysterious parentage. So, let’s find out more about corymbs and flower clusters. [And don’t let all the new words scare you off.]

Umbels and corymbs

First, we need to differentiate between umbels and corymbs. Umbels are flower clusters that look like umbrellas. The tiny stems, called pedicels, all emerge from a central stalk. Carrot, dill, and parsley flowers are all umbels.

​If a flower cluster has many branches, instead of a single point of contact, it is called a panicle. [But don’t panic! You can do this!]

​Flower clusters

Flower stems are called peduncles. As soon as the tiny stems of a flower cluster begin to emerge, that main stem changes its name to rachis [ray-kiss]. Each individual stalk within a flower cluster is called the pedicel. Each pedicel holds a floret. Pedicels can be arranged in pairs (parallel), or they can take turns (alternate).

Panicle (Shazz) CC BY-SA 3.0

Pedicels (Kate Russell)

Types of corymbs

Corymbs may be flat-topped or convex. This is because the tiny stems, or pedicles, get progressively longer as they move away from the center. If the pedicels of a corymb all emerge from the central rachis, it is said to be racemose. If there are several layers of branching rachis, it is called cymose.

Racemose corymb (Amada44) Public Domain

Cymose corymb (Amada44)

Cymose corymbs

Cymose corymbs are said to be determinate. Determinate inflorescences have a flower on the top that halts further growth. This top (apical) flower is the oldest one in the bunch. Younger flowers develop below this primary flower. Forget-me-nots, jasmine, and figs are all cymose.

Racemose corymbs

Racemose corymbs, or racemes, are said to be indeterminate. Indeterminate inflorescences are those with the oldest florets at the base and newer growth at the top. They just keep on growing. Cherries and other stone fruits all have racemose corymbs. Snapdragons and yerba maté are also racemes.

The next time you look at a flower cluster, take a moment to see if it is built like an umbrella (umbel), if its branches are all connected to a central stem (raceme), or if there is a complex system of branches (cymose). This can help you make better use of the many plant identification tools available online.