The science of blue flowers
You would think that blue is just another color in nature's palette, but when it comes to flowers, it's much more complicated than that.
Sat, Feb 08, 2014 at 09:15 AM
There's a reason the intensely blue orchid flowers you’ve seen in the floral departments of groceries, box stores and retail plant nurseries don’t look natural.
Blue isn’t a natural color in these types of orchids. These are white flowers that get their color from a dye used by plant breeders. “The identity of the dye and the process are patented,” said Ron McHatton, president of the American Orchid Society. Blue is a color that doesn’t occur naturally in orchids very often,” he added.
In fact, “blue is a color that is infrequent in nature,” said David Lee, who wrote the book "Nature’s Palette: The Science of Plant Color" before retiring in 2009 as a professor in the Department of Biological Sciences at Florida International University in Miami. “Less than 10 percent of the 280,000 species of flowering plants produce blue flowers,” he said.
Why is that? Why is blue seen so infrequently in flowers?
“There is no true blue pigment in plants, so plants don’t have a direct way of making a blue color,” Lee said. “Blue is even more rare in foliage than it is in flowers.” he added. “Only a handful of understory tropical plants have truly blue foliage.”
To make blue flowers, or foliage, plants perform a sort of floral trickery with common plant pigments called anthocyanins. Health food devotees will likely be familiar with anthocyanins because cyanidin-3-glucoside is a strong antioxidant, said Lee. “It is the most common anthocyanin in red leaves and red roses and is sold in the health food trade as C3G.”
The key ingredients for making blue flowers are the red anthocyanin pigments. “Plants tweak, or modify, the red anthocyanin pigments to make blue flowers,” Lee said. “They do this through a variety of modifications involving pH shifts and mixing of pigments, molecules and ions.” These complicated alterations, combined with reflected light through the pigments, create something that seems so simple on the surface: Color!
And the results are spectacular! Delphinums (right), plumbago, bluebells, and some agapanthus, hydrangeas, dayflowers, morning glories and cornflowers.
While we are most familiar with flowers in hues of yellow, orange, red, and purple, the relatively few that are blue don’t seem to deter pollinators. “Insects and birds can widely detect blue as a wavelength,” Lee said. What they are looking for is a reward — like food — and blue flowers are just as capable of producing that as flowers of other colors.
The real challenge with blue, said Lee, is in the horticultural trade where there is intense commercial interest in the chemical basis for blue flowers in nature. Many of our favorite garden and cut flowers, such as roses, tulips and snapdragons, do not produce blue flowers. One result, he said, is a determined effort to produce a blue rose.
Chemists have been able to use delphinidin, the pigment that makes delphiniums and violas blue, to make a purple rose, but they still haven’t been able to make a truly blue one, Lee said. The same is true with carnations, he added. “They still haven’t been able to push them into being blue.”
The method being used by horticulturalists to achieve truly blue flowers is different from the dye approach being used with orchids. They are using biotechnology to accomplish something unusual for the nursery trade, defying what Mother Nature discovered about biodiversity eons ago. Blue did not develop as a common color during the process of natural selection.
Lee, in fact, has created a presentation he gives to garden clubs and other groups that he has titled “The difficulty of being blue.” “I like to end those talks with a reference to Kermit the Frog’s song on ‘Sesame Street’ in which Kermit sings that ‘it’s not that easy being green’,” said Lee. “It’s even harder to be blue.”
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