Why Do Flowers Have Color? by Terry Foxx

Whether in a garden or a wild landscape, varying colors of yellows, reds, blues, and greens give us a sense of the earth’s innate beauty and complexity. We note the breathtaking red of one flower and the bright yellow of another and wonder why the difference. The simple answer is it is solely for reproducing. Without the interaction of birds, bees, and butterflies with flowers, it would be a rather colorless world.

Birds, bats, bees, ants, beetles, flies, butterflies, and other insects are responsible for reproduction in certain flowers. This is called biotic pollination. Flowers have evolved characteristics over time to attract certain organisms that act as pollinators. In addition, flowers can be pollinated by wind and water: this means of pollination is called abiotic pollination.

This relationship between the pollinator and the plant is essential for survival and health of pollinators and plants. Pollinators are responsible for assisting 80% of the world’s flowering plants! Disappearance of one can affect the survival of the other.

Over time flowers have evolved characteristics such as color and structures to attract certain organisms that act as pollinators. Colors come from various pigments in the flower. Carotenoids produce yellow, orange, and brown colors. Anthocyanin produces red, pink, blue, and purple colors.

So here are some of the relationships between flower color and shape that have evolved for the purposes of pollination.

Beetles: Beetles are essential pollinators but often not recognized as important. However, over 240,000 plants world-wide are pollinated by beetles. Unlike butterflies, bees, and moths, they eat their way through flower parts. They like flowers that are white to dull white or green with strong fruity smells. They rely on their sense of smell.

Beetle snuggled in the center of a Silverleaf Nightshade (Solanum elaeagnifolium). Photo by Terry Foxx
Beetle snuggled in the center of a Silverleaf Nightshade (Solanum elaeagnifolium). Photo by Terry Foxx

 

Butterflies: Butterflies are active in the day when the sun warms the atmosphere. They are attracted to flowers aggregated into a head of many small flowers that are red, yellow, or orange. The long tongue of the butterfly is adapted to sucking nectar from long-tubed flowers. Flowers attractive to butterflies have sweet scents and are usually blue, dark pink, yellow-red, and purple.

American lady butterfly photo by Selvi Viswanathan.
American lady butterfly photo by Selvi Viswanathan.

 

Bees: In a pollination contest, bees would be the champions! Their size and agility help them pick up pollen that is transferred from plant to plant. Bees generally frequent flowers that are blue or yellow or reflect yellow-green, blue-green, blue-violet, and ultraviolet light. Bee-pollinated flowers have a “landing pad” such as two-lipped (bilabiate) flowers such as in the Fabaceae (Pea family). Bee-pollinated flowers have sweet, pleasant scents and are full of nectar. The flower often will have lines or a different color in the center to guide the bee to the nectar location. Bees collect pollen as a protein source to feed larvae. The relationship is complex, since some flowers secrete nectar only at specific times of the day when fertilization takes place; bees visit only at that time.

Bee visiting a buttercup. Photo by Selvi Viswanathan.
Bee visiting a buttercup. Photo by Selvi Viswanathan.

 

Moths: Pollination takes place during the day but also the night. Moth-pollinated flowers are generally dull in color or white, open late in the afternoon or night, and are pollinated at night. Flowers often are tubular and pollinated by night-flying moths.

An example of a plant that has an interesting relationship with moths is Sacred Datura or Jimsonweed (Datura wrightii). Sacred Datura begins opening in the late afternoon, slowly unfurling until the funnel-shaped flower is fully open in the evening. The flower is visited by sphinx or hawk moths. They have a long proboscis which can reach into the nectary at the base. As they gather the nectar their heads become dusted with pollen. The narcotic nectar produced by the plant causes the moth to become “addicted,” so it solely visits the Datura. The hawk moth can be seen hovering over a plant waiting for the flower to open to get a fix.

Sacred Datura flower photo by Terry Foxx.
Sacred Datura flower photo by Terry Foxx.
Hawk moth, a pollinator of the Sacred Datura. Photo by Paul White.
Hawk moth, a pollinator of the Sacred Datura. Photo by Paul White.

 

Birds are attracted to flowers that have tubes, funnels, or cups and petals that spread outward. Hummingbirds are important pollinators within the United States but other birds in other regions can be pollinators. Examples are honeyeaters and honeycreepers in Hawaii and Australia. Generally hummingbirds are attracted mainly to red flowers but also to yellow or orange flowers. When they thrust their bill into the flower, their head becomes dusted with pollen, which is then transported to the next flower. Bird-pollinated flowers do not have a scent but have abundant nectar. Birds have a poor sense of smell but good eyesight. Plants that are red such as the Skyrocket Gilia and Scarlet Bugler are sometimes called “hummingbird flowers.”

Hummingbird on a Beebalm (Monarda spp.) Photo by Selvi Viswanathan.
Hummingbird on a Beebalm (Monarda spp.) Photo by Selvi Viswanathan.

 

Ants: Ants love nectar and often visit plants to collect the energy-rich nectar. They visit low-growing plants, often with inconspicuous flowers. The flowers are usually close to the stem.

Ant on a Poison Milkweed (Asclepias subverticillata) Photo by Terry Foxx.
Ant on a Poison Milkweed (Asclepias subverticillata)
Photo by Terry Foxx.

 

Wind-Pollinated Flowers: Wind-pollinated flowers are generally not showy and include plants like grasses, some trees, and weedy species. The male flowers may be in pendulous catkins. An example would be Boxelder Maple. In our area the best example is the juniper. The light pollen can be blown on the wind and travel many miles; it is called pollen rain.

Resources:

http://www.fs.fed.us/wildflowers/pollinators/
http://bioimages.vanderbilt.edu/
http://southeastgarden.com/pollination-the-purpose-of-flowers

One comment on “Why Do Flowers Have Color? by Terry Foxx

  1. Terri’s article is wonderful. I have another thought to add to why flowers have color.
    Because leaves are green! And why are leaves green? Because the sky is blue!
    It goes like this–tiny dust particles scatter blue light from the sun high in the atmosphere and so it doesn’t get to the ground as intensely as it would–same with violet light. Plants collect yellow and orange light for photosynthesis and reflect green and blue light. But there isn’t much blue light to reflect and so leaves reflect green light. Flowers need pollination by insects and so must stand out from the leaves to be found easily. So most flowers are yellow (the next color in the spectrum after green)! Of course some flowers reflect the other colors also to distinguish themselves from the yellow ones largely because some pollenators look for reds and blues instead of yellows. So there you have it. Flowers aren’t green because leaves are, because the sky is blue! Note that there are green flowers like grasses but they are wind pollenated and so don’t need to stand out. Things don’t just happen–they have reasons.

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