Anthocyanins: How Flowers Get Their Color - Science ABC

Where Do Flowers Get Their Color?

Plants get their colors from pigments it produces. These pigments are molecules that selectively absorb or reflect certain wavelengths of light. The wavelength it reflects is the color we perceive. There are a myriad plant pigments, but we can largely categorize them into four different types.

The most popular and the most common pigment in plants might be chlorophyll, providing plants with their green color. Most chlorophylls absorb red and blue wavelength light, mostly reflecting green wavelengths. And that’s what we see. Chlorophylls, though a plant pigment, aren’t commonly found in flowers. Their place lies in leaves and stems.

The second group broadens our plant pigment palette, introducing yellows, oranges and red into it. Carotenoids are the same pigments that impart color to carrots (hence the name), tomatoes, and sunflowers. A common carotenoid, ß-carotene gives sunflowers its optimistic yellow. It primarily absorbs light in the blue region of the visible spectrum, giving us a sunny yellow.

The exciting reds, purples, blues and pinks are the result of anthocyanins. These pigments belong to a class of flavonoids, and are the most important plant pigments for flower coloration. Flavonoids are a large group of compounds, scientists have discovered over 9000 different flavonoids, which are responsible for a range of colors.

Anthocyanins are the molecules that give petunias and orchids their enticing pinks, lends the lilac color of common lilacs, gives roses their passionate reds, and colors blue cornflower, well, blue. A type of flavonoid, tannins, also give tea its brown color.

Betalains color flower petals red to red-violet colors. These pigments give opuntia (or cactus pear) its red color and beets its beet reddish-purple shade. They replace nature’s popular pigments, anthocyanins, in Caryophyllales which include carnations, beets, cacti, amaranths and even some carnivorous plants.  

Just like painters mix colors to create a unique hue, the color of many flowers are a result of a combination of pigments in different proportions. This creates gradients and patterns within the flower.

These pigments are chemicals, and their color imbuing capacities can be changed by the pH, association with certain minerals such as iron or magnesium, and temperature. An interesting example of this is the coloration of roses and blue cornflower. The colors of both the flowers are caused by the same anthocyanin, the red and the blue. A 2005 paper published in Nature found that the blue is the result of a ‘superstructure’ of 6 pigment molecules associated with magnesium, iron, and calcium ions. This is fascinating color manipulation!

The color of a flower is decided by the hereditary genome of the plant to which it belongs; therefore, the color of the flowers of a plant is decided long before the flowers are born. Plant DNA has information to create certain machines, or enzymes that catalyze changes to the various organic molecules, creating the host of pigments we have today. You can think of it as a chemistry lab within every flower, with DNA as the instruction manual!