Inflorescences

Inflorescences. Flowers are presented in space and time in a way that optimises pollen transfer and fruit development. This is species-specific and under close genetic control. Some plants have solitary flowers but many have flower clusters called inflorescences. The location and shape of the inflorescence affects the reproductive success of the plant. Although there are a huge number of architectures that could arise there are only a few that have evolved in nature. However inflorescences are complex and there are many botanical terms used to describe them. In recent years advances in genetics and electron microscopy has led to a better understanding of how inflorescences grow.

poppy solitary flower

Solitary flowers are single flowers that are  not part of an inflorescence. An example is the Common Poppy. 

clematis peduncle pedicel

An inflorescence  is the botanical term for a flower cluster and it includes the flowers, pedicels and peduncle. 

horse chestnut inflorescence

The Horse Chestnut has a large inflorescence with many flowers and a complex branching system.

apical, lateral meristem

The development of the inflorescence is controlled by a group of cells at its growth point, called meristems. There are two types of meristems, an apical meristem and one or two lateral meristems.  There are two forms of inflorescence. In racemose growth the apical meristem continues to elongate the main stem and one or both of the lateral meristems produces a flower. This is known as monopodial growth. In cymose growth the apical meristem switches from stem growth to production of a flower and a lateral meristem takes over the role of stem elongation but at a slightly different angle. This is known as sympodial growth.

foxglove racemose growth

Racemose, monopodial growth.

racemose growth

At each node the main stem continues to grow and flowers are generated by lateral meristems. Foxglove

petunia cymose growth

Cymose, sympodial growth. At each node, the main stem meristem generates a flower and a lateral meristem continues stem growth.

petunia cymose growth

Detailed photo is of node 3. Petunia.

Types of Inflorescence

Raceme is the basic racemose structure. Spike is a raceme but with sessile (no stem) flowers. Panicle is a raceme with a branched racemic stem at each node. Corymb is a raceme with different length flower stems. Umbel is a raceme but with all flower stems are from the same point with different length stems. Capitulum is a flattened raceme.

 

raceme
spike
panicle
corymb
umbel
capitulum

Cyme is the basic cymose structure. They may be monochasial, with one lateral flower or dichasial having two lateral flowers.  Monochasial cymes differ in shape depending on whether successive lateral flowers are on the same side or on alternate sides. The shape of the inflorescence depends on the change in direction of the new stem. The result may be a flat shape or a 3-dimensional shape. Scorpioid or helical cymes are typical 3- dimensional shapes . A compound cyme has a branched cymose stem at each node. Numbers show the order of flower formation and opening.

monochasial cymes
dichasial cymes