Why do flowers have so many colors?

Edward Narbonne, Pablo de Olavide University

There are over 300,000 species of flowering plants pollinated by animals. Each of them produces flowers of a unique color in nature, which creates an immense and at the same time bewitching color range. The bright coloring makes the flowers stand out against the green background of the leaves, which allows them to successfully attract pollinators. Let’s see how.

Floral pigments are a great evolutionary invention

People thrive by imitating what happens in nature. While artists use natural or synthetic pigments to capture their ideas on white canvas, plants produce them themselves to paint their flowers.

The flower color is usually found in the petals, which are nothing more than layers of cells where pigments accumulate. One of the most interesting aspects of these colorants is that even in small amounts they have a great ability to absorb some of the visible light coming from the sun.

Thus, when sunlight hits the petals, some is absorbed by the pigments and some is reflected. For example, we perceive the red color of poppy petals because they reflect only the red part of visible light and absorb the rest.

In addition to green chlorophylls, which are relatively rare in flowers, there are three main groups of flower pigments:

• carotenoidsresponsible for the orange color of carrots, usually give yellow tones, as is the case with daffodils, sunflowers, marigolds or acacias.

• betalains they give the characteristic red beet spot. These pigments are found only in the cactus family and other related ones, where they produce yellow, pink, or reddish colors.

• flavonoids They constitute, without a doubt, the most common group of pigments, giving the colors the largest range of colors. Among them are anthocyanins, the queens of pigments, as the vast color palette they produce ranges from aquamarine blue to purplish black, fading into purples, pinks, oranges or reds.

Other flavonoids, such as flavonols and flavones, are colorless to humans because they absorb ultraviolet light and we cannot perceive it. However, the main groups of pollinators – mostly bees, flies, butterflies or birds – have visual systems that allow them to see this type of light.

In flowers, these compounds are part of the floristic landmarks. Although they are generally invisible to the naked eye, they are useful for pollinators to find nectar or other flower rewards.

A flower may contain one or more types of pigments. When it contains more than one, they can accumulate in the same area, creating a new color through mixing. In addition, dyes can be located in different parts of the flower and generate extremely complex color patterns, as is the case with many orchids.

How to get a lot of flowers

Although only these large groups of pigments exist, the variety of colors they produce can be enormous, as their basic structure can undergo almost endless molecular modifications. For example, over 600 types of carotenoids and anthocyanins have been documented, differing in their chemical structure.

In addition, anthocyanins can molecularly bind to metals or other flavonoids and produce intense colors such as the blue of a cornflower flower. This hue, so rare in wildflowers, could be very showy and attract bees.

As if that weren’t enough, other processes resulting from the reflection of light on the petals can increase the range of colors. For example, in the California poppy, the cells on the surface of the petals are ribbed, which enhances its yellow-orange color and gives it a characteristic silky sheen.

Even more surprising is the case of the Venus mirror orchid, in which the cells in the central region are so flat that they emit a very powerful white glow, creating a mirror-like appearance.

Attention Tournament

In the course of their evolution, flowering plants have developed mechanisms that favor pollination between the same species and thus avoid the deposition of foreign pollen. A certain color may be a mechanism for this. loyalty pollinators to visit plants of the same species.

On the other hand, there are periods in plant communities when many species flourish simultaneously. They generally share the same pollinators, which creates competition between plants to attract them.

As a result of this rivalry, plants have developed flower colors that differ from each other more than would be expected by chance. It has been found in grasslands in areas as diverse as Australia, North America or northern Europe.

However, not everything is known about the evolution of flower color. In a recent study, it was shown that anthocyanins, the most commonly found pigments in them, are not the most vibrant for pollinators. Therefore, there must be other environmental or evolutionary factors influencing the production of floral pigments.

Flowers and their colors still hide great secrets from us. Finding them is undoubtedly a big challenge that we must accept in order to better understand the relationships of plants with the environment, even more so in the current context of biodiversity loss.

Eduardo Narbona, Professor, Department of Molecular Biology and Biochemical Engineering, Pablo de Olavide University

This article was originally published on The Conversation. Read the original.

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