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Blue thou art… whence came thy dazzling hue?

Blue flowers are the RAREST color. I’ve noticed this for a long time. And it makes sense. But it is also confusing and weird and beautiful.

blue poppy.  blue flower. Meconopsis betonicifolia
blue Himalayan poppy (Meconopsis betonicifolia)

TLDR: Flowers are blue through difficulty for the plants, but because it draws more animal pollinators and they show up more in areas with steeper competition for pollination. And we are a bit obsessed with them and their color, despite seeing less than bees can.


Blue, not plum or lavender:


What stands out the least against a background of green for attracting pollinators to your flowers? Greens, browns, and blues. If we lived on a planet where photosynthesis used an orange compound, then I hypothesize that the most common flower color would be blue as the “complementary color” pair (red-green, and yellow-purple). These are the most opposite and thus balancing and contrasting of color pairs, just basic color-theory. Well, that's a scifi world. In reality, it's actually not about what we see best against green, or at all even.


Blue is the Plant Minority & We Can’t Stop Loving It:

slender bog orchid. green flowers.

Though instinctively, we can see blue doesn’t contrast too well with green foliage, so that should make it less advantages to use for plants to show off their flowers to pollinators. Yet green is even harder to see and there are a lot of green flowers. You may not have noticed them. Of course it's much more complex a scenario for plants than what's noticeable to us.


Not many notice these slender bog orchids in wet spots along PNW trails, but they have interesting little green flowers if you take the time to examine them.



Turns out it is also a bit more difficult for plants to make blue pigments compared to other colors. Why produce a more effective production pathway for a pigment if it doesn’t lend as much of a fitness boost? Well.... actually.... Apparently bees are all about blue. So, what's the deal? Do only certain plants step up to that challenge then to please the bees? Even then, not everything goes to plan... Pollination is risky business for everyone.

gilia flower and bee.  spider eating a bee on a flower
blue gilia flowers (Gilia capitata) with a honey bee that got snagged by the face by an ambushing spider.

Contrary to what some have said (yeah, I’ve heard it), bees CAN see blue and actually see more blue than our human eyes can perceive. Bees see blues, ultraviolet and greens and actually show a general preference for bluish flowers. They also have different light wave receptors. Oh yeah. Let’s get even more sciency! Bees have what’s called trichromatic vision using UV, blue & green receptors. We have trichromatic vision but with red instead of UV. Think bees can see us getting sunburned by UV? Bees' preference is for the shorter wavelengths particularly in that blue range. Maybe it's just easier for them to see because it's the mid-level energy wavelength in their visibility.


So blue is harder for plants to make, but bees actually prefer it, and can see it better against the green plants than we can, so… why still so rare? Are they actually rare? Plants will only appease their nectar-collecting little visitors with more appeal if there’s enough competition to make the effort worth the cost to them. The frequency of blue flowers increased in harsher environments like in the Himalayan mountains and likely where competition for the pollinators is higher, shorter seasons to bloom. Some research has also found that blue flowers are more nectar-rewarding to bees as well, like a wealthier plant able to make that costly color AND yummier food for their pollinators. This feels like the scenario when your romantic partner mentions a fun new coworker who is also very attractive, and you’re getting a little jealous with some possible competition, so NOW it’s time to go buy some new (expensive) lingerie and arrange some more occasions to wear it. And yes, there is male-body lingerie (finally!) and I’m so happy about that, but that’s not the topic here. Blue bee balls... yes- focus brain!

Point is- competition means plants will put in more effort. Or they may not pass on their genes. Basic natural selection, via flower color for pollution competition.


While flowers WE see as blue are generally rare (except under high-stakes pollination areas), some flowers do have blue signals to pollinators often as a “blue halo” around the center of their flower like a ‘come hither’ signal to a blue-seeing bee, guiding them to the actual reproductive parts. Some bees need a guide, what can we say. They may be visible to us on the blue spectrum, or just refracting a blue wavelength to the bee eyes, called “nanostructures”.

blue ring in flower
science.org picture by Edwige Moyroud of blue nanostructures on flower

One survey of flowers by human-perceived colors:

“Global flower colour frequency for human visual perception (A) shows when considering animal pollinated species less than 10% are blue (B), and for wind pollinated flowers almost none are observed to be blue (C)”


These numbers do seem iffy with the conclusion of the paper that blue is the rarest. I suspect they were grouping reds with pinks and maybe oranges with yellow. Many of those colors are fairly subjective as to the precise color, much like blue is. Blue or blueish purple??


In this survey of flower color frequencies, blue was among if not THE rarest, though not among specifically animal-pollinated (aka entomophilous) flowers. Blue never shows up in wind-pollinated (aka anemophilous) or other abiotic pollinated flowers. Even some non-animal pollinated flowers are red, oddly. Wind does not see any color, bees and other insects and birds do.

blue-eyed Mary flowers. blue-named flowers. Blue flowers.
large and small "blue-eyed Mary" plants (left & right) which are really more purple, with a small forget-me-not (Myosostis discolor) that is both blue and yellow, hiding behind them

And likely the above survey, which used an online database of flowers by trait, probably had a mix of purplish-blue flowers in the "blue" category. Many flowers with "blue" in their name are actually more a lavender or plum color.

blue-eyed grass flower, sisyrinchium sarmentosum
Sisyrinchium sarmentosum (aka pale blue-eyed grass), also not a grass (iris family)
Still, the studies have shown, blue is rarest.

So animal pollination is driving the evolution of blue flowers. On top of that, more flowers appear blue to a bee or butterfly than they do to us. This leads to the question- what IS blue anyway? If we see it differently from bees, what is the ‘real’ blue? Then there’s the whole issue of some color blindness in a surprising percentage of people, and the argument I’ve had with people about a blue rug that they thought was for sure black. Aren’t we fascinating?!

Favorite new word: Psychophily = pollination by butterflies

Humans have also been fascinated with blue colors for thousands of years, going great lengths to create blue paints and fabric dyes. Blue is even what the majority of people sight as their favorite color (sshh, it’s not mine, but I still like it for interior wall colors and the soothing mood it creates around the house, and then there's the Dr. Who theme….)

blue walls
Dr. Who blue
















Wondering which color is people’s least favorite? Yellow. At least for flowers. And the second most common, go figure. Does the collective ‘we’ love it because it’s rare, like a first issue comic book? Or is it naturally inviting and soothing because bright blue sky & water indicate a healthy safe place to be? Some experts do think this may be the case, but only a sentient alien species or terribly unethical human experiment could test this, so let’s stick with- maybe!

blue penstemon on sand dune. Penstemon acuminatus
Blue penstemon (P. acuminatus) in the sand dunes of east WA under bright blue sky

What makes plants blue?

You’ve probably heard of chlorophyl for the green photosynthesizing pigment of plants. And carotene for the oranges of carrots (sounds close). Most plants like “blue”-berries are actually a deep purple that our eyes perceive a bit like blue, which is from an anthocyanin pigment, also responsible for red and purple colors. Anthocyanins are responsible for the blues, purples, reds and ever the nearly black-looking color like blackberries have. The way plants synthesize the anthocyanin is what determines what of these red-blue hues are created. The blue anthocyanin (delphinidin) also require a slightly acidic or neutral pH in the plant cells. Some species stack several pigments or include metals in the production of their blue pigments. And Kermit thought it wasn’t easy being green! If you’re a plant, blue is harder. The more true-blue colors in flowers and butterflies is a combo of pigments and some fancy physics of light refraction making US see more pure blue. It’s more like the other colors of visible light are getting canceled out so we’re left with a mix that looks blue.

blue flowers
Deep blue hydrangea flowers, by Ruma Views

As more recent studies have found, blue as seen by bees (the short wavelength refraction) is actually quite common. Wish we had bee-goggles to see the natural world as they do. Some have simulated it though.


bee's view of flowers
yellow flower as seen in UV and by likely bee-vision, by RMIT University Sue Williams and Adrian Dyer

Blue flowers are only found in 53 of the known 406 plant families (and 372 or 14,038 plant genera), only including flowering plants (no conifer trees which would not need any blue cones as cool at that would be). Several are famous garden cultivars treasured for their brilliant blue (see hydrangea post).

blue hydrangea flowers.  blue flowers
blue hydrangea flowers in the garden

Others feeling true-blue:

Veronicas

Gilia (also blue pollen!!- Polemoniaceae family has several species with the “blue ball” trait, bee-keepers been confused)

Meconopsis/Himalayan poppy (Meconopsis betonicifolia) *alpine & Himalayas… remember?

Bluebells

African violets

Cornflower

Agapanthus

Hachelia spp., Hounds tongue species (Adelinia spp) & Forget-me-nots (never…)all in Boraginaceae family.

blue flowers
agapanthus flower, by John Campbell

Kind of makes you want to plant a blue-themed garden, doesn't it. Finding any of these or other true-blue flowers in the wild should feel extra special now. They put extra effort into creating that pigment and it's special we can even see it as blue. Because it's really for the bees & butterflies out there. We're just spectators in the grand theater of plant ecology.

Hachelia taylori flower
lab-grown rare plant Hachlia taylori of Washington
pentaglottis sempervirens flower
green alkanet (Pentaglottis sempervirens) weed

References:

- https://www.abc.net.au/news/2021-01-25/the-mystery-of-the-blue-flower-natures-rare-colour-bee-vision/13083216

- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4906640/

- https://www.nature.com/articles/nature24285

- Dyer, A. et al., 2021. Fragmentary Blue: Resolving the Rarity Paradox in Flower Colors. Front. Plant Sci. Vol. 11. https://www.frontiersin.org/articles/10.3389/fpls.2020.618203/full

- Streinzer, M., Neumayer, J., and Spaethe, J. 2021. Flower Color as Predictor for Nectar Reward Quantity in an Alpine Flower Community. Front. Ecol. Evol. Vol 9. https://www.frontiersin.org/articles/10.3389/fevo.2021.721241/full



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