Why are so many early flowers yellow?
March 9, 2016
I visited Arizona recently and the desert was blooming. The predominant color of flowers, no matter the type of plant was yellow. I wondered why nature has given us so many early blooming yellow flowers, particularly in the daisy or sunflower family. This family (Asteraceae) is one of the largest with about 25,000 species and a broad distribution worldwide. In fact, botanists are known to call the multitudinous daisy family members "damn yellow things" because they can be challenging to identify since there are so many of them. With such a prolific family, we do see lots of these DYT. The mustard family (Brassicaceae) also produces many early blooming yellow-flowered plants including flixweed and tumble mustard, two prevalent and annoying spring weeds.
While we as gardeners may plant flowers for their color to please ourselves, the real reason flowers are a certain color is to attract their specific pollinator who will spread pollen from flower to flower. When pollinators, such as bees, go in to eat, they collect the male pollen on their bodies. As they move to another part of the flower or as they fly to another flower, they then spread the pollen to the eggs. Fertilized eggs allow the flowers to produce the seeds necessary for continuation of the species.
However, insects do not see color in the same way we do. "Many flowers have ultraviolet patterns, invisible to humans but visible to insects such as honeybees… (Gronquist et al, 2001). Yellow flowers actually appear blue to bees and other pollinators. The UV blue appearance of the flower highlights the center as if it were a bull's eye, directing the pollinator to the pollen or nectar source. A blue bull's eye makes the flower more attractive and more obvious to the pollinator. Perhaps the pollinators that come out early in the season need help finding the flowers in an area as they emerge groggy from hibernation. Nature's yellow coloring may provide that bull's eye effect to say, "Come and get it. Here we are!"
While we are on the topic of pollinators, you may want to read Dr. Heidi Kratsch's publication "Flowers at the Border – Plant native flowers around your yard to attract pollinators and other beneficial insects." It is available at http://www.unce.unr.edu/publications/files/ho/2014//sp1407.pdf or at your local Cooperative Extension office. She has compiled a comprehensive list of native perennial flowers with descriptions and growing tips.
JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at firstname.lastname@example.org.