Plants with the most complete spectrum of flower colors

[Lee Poulsen]

One of the things I started reading early on in my plant hobbyism was that some plants had varieties with flowers from "almost" the entire spectrum or rainbow of colors. Then after stating that they'd continue to mention the one (or more) colors that were missing. One of the famous ones is the rose. And the color most often mentioned as missing was always blue. And some would mention the closest to blue that had been produced but that were really a kind of purple or lavender or mauve. I think even the Japanese tried to create a "true blue" rose by genetic manipulation, by inserting genes from some other flower that really did come in a true blue color (like delphinium I think). What they ended up with was yet another lavender rose, although a very different shade of lavender than the traditionally bred ones. Apparently there was a problem with the acidity of rose petals that altered the color of the blue genes they'd introduced. They also tried it with carnations, probably because most people weren't fooled by the "blue" carnations produced by putting white carnations in solutions of blue dye. In that case the Japanese produced some beautiful lavender and purple carnations, a color I don't think existed for traditionally bred carnations. (Google the "Moonseries" carnations.) Another genus, and much more geophyte related are Irises. And indeed, I think the word Iris means "rainbow" in Greek.

But I think when those are mentioned, many people leave out parts of the spectrum, or rather "color wheel", that humans can see and recognize, but are sometimes skipped or ignored, I'm not sure why. So I'm just going to review the basics of the color spectrum or "wheel", so that I can then post my claim as to the species that has flowers that cover the full spectrum most completely. (And it happens to be a geophyte! ) So the three primary colors of projected light, think a color flatscreen TV or computer monitor, are red, green, and blue. And from those three when used in various mixtures and relative intensities, they derive all the other colors we can see. The three "secondary" colors, which are sometimes called the three reflected primaries, think color prints made by color laser printers or printing presses which, if you have one, you know have three color toner cartridges, yellow, cyan, and magenta. Using those three, used in various mixtures and relative intensities, they can likewise derive all the other colors we can see. Even more interestingly, if you are using the light primaries, mixing equal intensities of red and green produces yellow light, green and blue produces cyan (or "teal") light, and blue and red produces magenta light. Which are the three reflective primaries. While mixing equal amounts of yellow and cyan/teal toner produces a green color, cyan/teal and magenta toner produces a true blue color, and magenta and yellow toner produces a real red color, which are the three light or projective primaries.

[Side note: color laser printers usually have at least 4 different toner cartridges, the 4th one being black (leading to the acronym CMYK, where the K is for black). The reason being that technically, mixing equal amounts of yellow, cyan, and magenta should give black, but it is usually a vary dark muddy brown. Plus, black toner is much cheaper than color toner and it uses ⅓ as much toner since you only use one unit of black instead of 3 units of each of the 3 more expensive toners. The analog of mixing the three reflective primaries to produce black is that when you mix the three light, or projective, primaries of red, green, and blue in equal amounts or intensities, you get white. Which is how it is done on TVs and monitors. You only ever have RGB, not RGBW.]

And before I get to my nominee species, I want to throw out just a few more colors, and I don't know what to call these. But they seem to be colors that are neither primary nor secondary, but that many humans seem to think of as their own independent color. For example orange. Many people do not see "true" orange as either a shade of yellow or red, or even yellowish-red, or reddish-yellow, but as "just" orange. Same with purple or violet. It's not a shade of blue or red or even magenta. And speaking of magenta, I'm going to include pink in with magenta as a less intense or maybe slightly lighter magenta. It's not "light red". (Try making "light red" with your computer by selecting red, then reducing the intensity of it. You don't get pink.) And finally, an odd one that isn't on the edge of the color wheel, which is brown, as in chocolate brown. It's basically a darkened red-orange-yellow, depending on what shade of brown you're talking about, but "chocolate" brown seems to be the standard brownest brown.

[One more side note: The rainbow or the spectrum does not contain all the colors the human brain recognizes or interprets as different colors. On the scientific standard for color, the "spectral colors" form a somewhat odd-shaped curved arch, from red through orange, yellow, green, cyan, and blue. Then they connect a straight line from one end of the curved arch to the other and call this the "line of purples". It contains the purples/violets and magenta shades. It's interesting because you can't produce these colors in people's brains using just one frequency of light--as you can with all the other colors along the "spectral" color curve. You have to use at least two different frequencies of light in different relative intensities to get the purples and magentas, even though the mind interprets it as a single color. This is why you will never see purple or lavender or magenta in a rainbow.]

Okay, and now to get to my nominee. Roses and carnations don't come in blues or teals, and true green roses I think are very rare and maybe there is only one species rose that comes in that color. Irises, in particular tall bearded types also don't come in teals or true greens, and a true red is still not there I think (although other Iris types have true red I think). Roses and irises do come in white, but not yet true black, although there are really dark purple-black irises, and dark red-black roses. There are certainly magenta and pink roses, but although there are pink irises, I don't think I've ever seen a magenta tall bearded iris. Irises win over roses for blue ones, even if not quite as intense and true blue as gentians or Tecophilaea. There are some fairly chocolatey brown irises, and some more muddy looking brownish roses. And of course teal flowers are incredibly rare, rarer than green flowers IMO. The ones I know about are two geophytes, Ixia viridiflora and Lachenalia viridiflora; two Puyas, P. alpestris and P. × berteroniana; "Jade Vine", Strongylodon macrobotrys; Ecbolium viride; and maybe one or two others I can't think of right now.

So for the most complete spectrum of flower colors, I nominate Anigozanthos or kangaroo paws, ever since they bred the teal-to-blue colored 'Masquerade' variety--which I've now seen in person, and a very nice member of PBS saw for sale up in the San Francisco Bay Area and sent me some. Yes, they have now been imported into the United States, it appears. And they really are the color you see in the photos. I think kangaroo paws may include every major color around the entire spectrum now. Meaning, red, orange, yellow, green, teal, blue, purple, magenta/pink, and also white and black, (and may some not quite chocolatey browns). Here are some links to photos out there on the web. See if you agree.

red: <https://1.bp.blogspot.com/-ISfJMmfys48/XNzV0ez1QbI/AAAAAAABnzI/QlY4iEW3LPcVwwh3NVhtMvUgYt2RXhKfwCLcBGAs/s1600/DSC07905.JPG>
scarlet red: <https://www.gardeningwithangus.com.au/wp-content/uploads/2017/05/anigozanthos_kangaroo-paw_landscape-scarlet-1.jpg>
orange: <https://www.ranchotissue.com/wp-content/uploads/2015/06/AnigozanthosTequilaSunrise1.jpg>
yellow: <https://www.gardeningwithangus.com.au/wp-content/uploads/2015/12/anigozanthos-flavidus-x-pulcheremis_kangaroo-paw_yellow-gem-1.jpg>
yellow-green: <https://www.ramm.com.au/wp-content/uploads/2021/11/Aussie-Spirit-1.jpg>
green: <https://www.gardeningwithangus.com.au/wp-content/uploads/2022/06/anigozanthos-viridis_kangaroo-paw-2.jpg>
teal: <https://www.thejunglecollective.com.au/wp-content/uploads/2022/08/Anigozanthos-Celebrations-Masquerade-Friends-of-Kings-Park-s.jpg>
blue: <https://thursd.com/storage/media/42427/Blue-Anigozanthus-on-Thursd-.jpg>
deeper blue ("true blue"?): <https://scontent-lax3-2.xx.fbcdn.net/v/t39.30808-6/281957091_10159664665337707_9178472396774143961_n.jpg?_nc_cat=101&ccb=1-7&_nc_sid=dbeb18&_nc_ohc=MbKNLQQjzL4AX_Zqcmd&_nc_ht=scontent-lax3-2.xx&oh=00_AfC8kql4TZa7yka77VTLzvGsvvNjqPMqX0E-Lgb0l90jCw&oe=648D2EBA>
purple: <https://nativeplantproject.com.au/wp-content/uploads/2022/10/anigozanthos-celebrations-'carnivale-pbr-1-568x764.jpeg>
magenta/pink: <https://www.benaranurseries.com/media/catalog/product/cache/29075eb501be649b1cefe83d67182d6c/w/e/website_anibusgempea5.jpg>
white: <https://gardenworld.com.au/wp-content/uploads/2020/05/kangaroo-paw-white.jpg>
black: <https://www.nurseriesonline.com.au/wp-content/uploads/2023/03/Black-Kangaroo-Paw-flower.jpg>
brownish (a pure species): <https://www.gardeningwithangus.com.au/wp-content/uploads/2015/12/anigozanthos-kalbarriensis_cats-paw-1.jpg>
yellowish-reddish-brown?: <https://cdn.shopify.com/s/files/1/0634/0997/9621/products/Anigozanthos_695x695.jpg?v=1682341244>

[David Pilling]

An experiment I have always wanted to do is measuring the spectrum of light from flowers. From the spectrum one can determine the chemicals involved. I often feel that the colours of different species are the same, and that's probably because they are using the same chemical.

Flowers might produce colours from pure single chemical spectra or by combining them. I'd imagine it is easier to manipulate the colours of flowers that result from a combination of base colours.

An interesting thing is that when you see yellow you might be looking at a pure yellow light, a light of a single frequency or two lights combined at the frequencies of red and green.

Presumably there are other ways of producing colours in flowers - thin film effects, like the colours of the rainbow on the surface of oily water.

[Lee Poulsen]

An interesting thing is that when you see yellow you might be looking at a pure yellow light, a light of a single frequency or two lights combined at the frequencies of red and green.

This is very true. And apparently pure spectral yellow and yellow made from red and green are indistinguishable to humans, but don't look anything alike to flies. I learned that if you want to use the low-tech solution to get rid of flies of using flypaper, you have to be sure that the flypaper color is single frequency yellow rather than a combination of other frequencies. Because flies will not be attracted to non-single frequency yellow flypaper.

[Steve Marak]

Lee, this is very interesting. I've been fascinated by color since I heard a talk by an ornithologist who was studying the visual system of birds (this was back before I paid much attention to birds, so I don't recall now why I was even there). He showed examples of colors that looked identical to most humans, but were composed of different frequencies of light and look very different to birds. Many birds are tetrachromats, with different color sensitivities than ours, including into the ultraviolet.

I started casually following the efforts of plant breeders, and in some cases gene shufflers, to achieve colors not found in nature, such as the blue rose or blue Phalaenopsis orchid (which was modified to produce the blue pigment in Delphiniums). But I hadn't considered the question you asked, which is a great one. And I like your answer! I've seen pictures of 'Masquerade'. If only I could keep Anigozanthos alive.

David, re your question of other ways to produce color than pigments, some plants also produce "structural color", derived from the way light interacts with nanoscale structures. (As do some birds and insects; I've read that all blue color in bird feathers is from structure rather than pigment.) I've been slowly accumulating research papers on this topic for years, and still don't have very many.

You also reminded me that I saved a couple of papers on how to use a cheap plastic diffraction grating and the standard camera in a smartphone, with some software from the Android app store, to make a spectrometer. I need to dig those out and actually try it. One more project for my overflowing list.

Steve