How flowers get their colours

Have you ever wondered how flowers get their colours – why roses are red and violets are blue? Science and evolution play a vital yet fascinating role in creating each flower’s unique colours, which help plant species survive.

How flowers get their colours

Pigments determine a flower’s colour

DNA is responsible for each flower’s unique colour. Each plant’s genes direct cells to produce pigments of various colours. These pigments are molecules that selectively absorb or reflect specific wavelengths of light. The colour we see is the wavelength it reflects. For instance, when a flower is red, the cells in the flower’s petals absorb all wavelengths of light except the one that produces the colour red.  

There are many plant pigments, but they’re primarily categorised into four different types. The most common plant pigment is chlorophyll which gives plants their green colour. However, you won’t usually find the chlorophyll pigment in flowers but instead in the plant’s leaves and stems.

The second plant pigment category is carotenoids, which reflect yellow, orange, and red. This pigment is what gives sunflowers their cheery yellow colour and marigolds their rich orange hues.

Anthocyanins are the vibrant coloured molecules that are the source of reds, purples, blues, and pinks. All these pigments belong to a class of compounds called flavonoids which constitute the largest group of water-soluble pigments in the plant kingdom. Scientists have discovered over 9000 different flavonoids that are responsible for producing a range of colours. Anthocyanins give lilacs their soft purple hues and produce orchids’ vivid pinks.

The last main pigment category is betalains, a group of red and yellow tyrosine-derived pigments found in Caryophyllales – a large and diverse order of dicotyledonous flowering plants. Betalains replace nature’s most popular pigments, anthocyanin, in this order which give plants like beets and carnations their reddish-purple shade.

What about flowers with multiple colours?

Similar to the way painters mix paint colours to create a unique, the colours of flowers are determined by the composition of pigments which creates different gradients and patterns within the flower.

Interestingly, as pigments are chemicals, simple changes in the pH of certain minerals such as iron, magnesium and temperature can alter their colour composition. For example, roses and blue cornflowers contain the same pigment, anthocyanin, yet the blue colour in cornflowers is a result of a ‘superstructure’ of 6 pigment molecules associated with magnesium, iron and calcium ions.

Colours play a role in evolutionary survival

The colours of flowers serve far more significant purposes than for human enjoyment. The survival of each species depends on the colours of its flowers.

Flowers are the reproductive parts of plants. They attract pollinators by offering nectar and protein through their flowers. When the pollinators land on each flower, they pick up the pollen and transfer it to the other flowers and plants they visit, allowing the plant to reproduce. As most pollinators fly, the colours of a flower must attract them. That’s why most flowers a brightly coloured. Some flowers also produce pigments that can only be seen in the ultraviolet part of the light spectrum as bees can see these colours.

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