Why We See Flowers Have Color

Yellow colors and nectar attract bees to fertilize squash.

Master Gardener Scoop – May 23, 2018

Will Summers,
Master Gardener

This time of year we are beginning to see that arrival of brightly colored flowers and few of us may wonder about the significance of this process. Our ability to see flower color is no small feat. In fact, humans see colors that many other birds and other animals cannot. The ability to see is governed by the abundance of rods and cones in our eye retina.

Rods give us the ability for night vision and nocturnal animals such as cats, foxes, raccoons and deer have them in abundance, but they have poor color discerning ability. Cones give us the ability to see details in the light and to see colors. Animals that have the ability to “see” in the dark (or low light), have significant loss of the ability to see in color.

The human eye contains approximately 125 million rod cells and six million cone cells. Cone cells are located mostly in the center of the retina, while rod cells are on the outer edges. Humans may have 150 thousand cone cells per square millimeter, while birds with keen eyesight such as hawks will have up to one million cone cells per square millimeter. There are three types of cone cells. The ability to detect color is a result of a pigment called “photopsin”. Each cone cell has a photopsin with the ability to detect either red, green or blue colors. Color-blindness results from having a lack or disproportionate abundance of one or more of the appropriate color of cone cell.

Orange colors attract butterflies.

Some birds and insects also have the ability to see in ultraviolet light that we do not. Flowers also may augment their colors with sweet-smelling scents and sweet-tasting nectar. Many bright colored birds see in color, while most dull colored birds cannot.

No one can say for sure why birds, flowers and some animals are so colorful. There may be many reasons and other reasons that may never be known, but for flowering plants, one obvious benefit is to attract pollinators, especially insect pollinators. Color, that improved pollination, also improves reproduction. With improved reproduction comes increased survival! This has to have been beneficial, or else these plants would never expend so much energy in doing so. Different colors attract different pollinators. For instance, bees are more attracted to blue and purple, while butterflies are drawn to yellows and orange and hummingbirds are attracted to reds and pink flowers. This is also the reason why night blooming plants are generally white, the absence of color, but which contrasts the most under moonlight and starlight. Subsequently, flowering plants produce brightly colored petals that draw pollinators to brush against the male, pollen-producing anthers. They carry the pollen to the pollen receiver, the style, so that fertilization of the embryo will result. Approximately three-quarters of all plants rely on this phenomenon.

Why are all the plants green, you might ask? If you remember the light spectrum: R-O-Y-G-B-I-V, you’ll notice that the color green falls in the center of the visible light spectrum.

Why is that significant?

Because its location puts it in the center for maximum efficiency to power photosynthesis. Actually, when you see green, it is not because the plant cells actually absorb green light. Green reflects back into our eyes so the plant only appears green. All the other colors are absorbed into the leaf to power plant production of carbohydrates by photosynthesis. Consequently, the global, collective green plant growth accomplishes the production of approximately 13 billion tons of plant biomass on the Earth every day.

Seeing colorful flowers in springtime is no small feat. This spring, when the flowers appear, we hope you will appreciate how wonderful the usefulness that color is in the plant world and the ability to see all life in general.

Please direct gardening questions to your local University of Illinois Master Gardener, your local Extension Office, or visit your local Library.

Please come to the Washington County Master Gardener Spring Plant Swap, held at the Nashville Public Library parking lot on Saturday, May 26, 2018.