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In the (relatively new) Star Trek movie Into Darkness, we see Dr. Bones and Captain Kirk in a world composed mainly of red plants. Obviously these are just eye candy with no real basis behind it, but I would like to go further.

What conditions would be necessary to have plants red in color? Blue?


Some factors I would imagine would be very important in deciding the color of my plants:

  1. Sunlight — There a reason our plants here on Earth take most of the warm colors in more efficiently than green light. The color of our sun is yellow. Would having a green or blue sun impact the color the plants absorb?

  2. Soil content — a shifted soil content might affect a plants color. A common example here on Earth is flamingos. Obviously not plants, but the way they change color upon eating large quantities of shrimp is a good example.

Any other ideas welcome to be addressed!

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  • $\begingroup$ See worldbuilding.stackexchange.com/questions/15374/…, worldbuilding.stackexchange.com/questions/13703/… and links therein. $\endgroup$ – HDE 226868 Jan 21 '16 at 23:17
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    $\begingroup$ Plants on earth actually don't partake of the peak of the spectrum. They absorb violet light, while if it wanted the most energy it would go for the opposite. Some scientists think that they adapted this way due to a large amount of violet foliage. livescience.com/1398-early-earth-purple-study-suggests.html $\endgroup$ – Xandar The Zenon Jan 22 '16 at 1:48
  • $\begingroup$ According to my college education, the sun is actually green. ;) $\endgroup$ – Jon Jan 22 '16 at 3:47
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    $\begingroup$ Another thing to consider is that some plants and bacteria fluoresce in wavelengths we can't see (near-IR). The "color" something appears depends on what you can perceive. There are coatings that shift invisible (to humans) UV to blue wavelengths to give a "whiter than white" appearance. You might also check into thin-film interference which can have some interesting effects. If you want to go really alien, you have to think beyond pigments reflecting light I think. $\endgroup$ – ColleenV Jan 22 '16 at 5:18
  • $\begingroup$ Alien plants with red leaves?? Alien? I think not. $\endgroup$ – Joe Bloggs Jan 22 '16 at 14:56
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The colour of plants — or any other solar-powered autotrophic lifeform that may or may not be capable of description by the term "plant" — is a function of chemistry and evolution.

Put quite simply, there are only so many viable compounds that allow photosynthesis to take place in a given environment, and they vary in efficiency. Some may be faster than others, some may be more efficient than others, and some may be able to absorb and utilise a greater percentage of the incoming light than others. The latter is defined by colour.

On earth, leaves are green because chlorophyll reflects green light. Green light is a major component of sunlight, and since it is reflected not absorbed, it cannot contribute to photosynthesis. However, it is used by terrestrial plants just because. Because chlorophyll was a compound that worked, and it worked well enough, and nothing better came along.

An ideal, theoretical photosynthetic compound would be black, absorbing all of the incoming energy, however this would only realistically be achievable with a suitable mixture of different photosynthetic compounds. A better colour for a photosynthetic pigment on Earth would be red or purple, since the light output from the sun is less intense in these frequencies, but while red pigments such as phycoerythrin might be better, plants simply never used them.

So, you may have almost any colour, as long as its chemistry is feasible and nothing significantly better has appeared in the particular niche of the biome. "It just evolved that way."

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  • $\begingroup$ The contingency of evolution. Good answer! $\endgroup$ – AlexDeLarge Jun 28 '16 at 9:20
  • $\begingroup$ This is a pretty good answer, but I feel it makes an error. I agree that the particular photosynthetic compounds chosen by evolution is in large part random. The part I disagree with is where you discuss specific colors more appropriate to Earth. Chlorophyll is quiet effective because it absorbs both red photons and blue photons, the former having the numbers (light at the earth's surface peaks in the red part of the spectrum) and the later being the highest energy photons readily available in any quantity. Green (or yellow or orange) are very good colors for high-light Earth plants. $\endgroup$ – n_bandit Feb 15 '18 at 16:07
  • $\begingroup$ An answer I recently provided on this post (worldbuilding.stackexchange.com/questions/104580/…) I think might contribute something here. It also links to a NASA Goddard Institute for Space Studies article (ebscohost.com/uploads/imported/thisTopic-dbTopic-1033.pdf) that discusses at length what color schemes would be more likely on planets around particular star-types (F, G, K, M) and during different ecological stages. Black is only a likely common color around M-class stars and not likely around others for reasons of efficiency. $\endgroup$ – n_bandit Feb 15 '18 at 16:11
  • $\begingroup$ @n_bandit, If you look at the graph on en.wikipedia.org/wiki/Sunlight#Composition_and_power, you can see that after atmospheric absorption, sunlight intensity peaks in the green part of the spectrum. Evolution is not always "Survival of the fittest" but often "Survival of the adequate". While chlorophyll is not the most efficient photosynthetic substance, it works, and organisms using it never had to compete with organisms using anything better. - or if they did, other factors may have come into play. $\endgroup$ – Monty Wild Feb 16 '18 at 20:49
  • $\begingroup$ @n_bandit, interesting article... but it doesn't disprove that any adequate pigments might evolve and be adequate in the absence of anything better. Sure, water can be split using the energy from a red photon, and higher energy photons be stepped down in energy via absorption and emission, but a pigment might use high energy photons to split multiple water molecules with 1 photon, or CNOH chemistry might be supplemented with other chemistries such as Sulphur, resulting in different needs, such as photosynthetic splitting of hydrogen sulfide. The optimal colours of such pigments would differ. $\endgroup$ – Monty Wild Feb 16 '18 at 22:22
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The way I am reading your question, you are asking about the mechanism of photosynthesis in alien plants, which would affect the colour of the leaves (or whatever sunlight collecting mechanism these plants use).

On Earth, the primary pigment for photosynthesis is chlorophyll, and green chlorophyll pigments evolved to take advantage of the major component of solar radiation entering the Earth's atmosphere. Around different stars, the plants would preferentially absorb different wavelengths of light. Around a hotter star, plants may look yellow or orange (or possibly blue; reflecting away the more dangerous energetic radiation), while around redder stars, plants might become black. (see: http://www.solstation.com/life/a-plants.htm)

Other parts of the plants may still be colourful, in order to serve other purposes. Flowers and fruit are brightly coloured in order to attract pollenating insects, or animals to eat ripened fruit and spread the seeds, so if there are analogues to pollenating insects or mobile animals to spread seeds, then we might expect similar adaptations from the plants. Other colour codes include warnings that certain parts of the plant are poisoned. Other adaptations may be possible depending on the environment and how plants evolve to adapt to them.

Larry Niven popularized the "Sunflower"; a plant with a reflective coating to focus sunlight on a photosynthetic nodule. This might evolve in places where sunlight was very weak. Of course Niven's sunflower also could refocus the sunlight to burn competing plants and even herbivores who might eat the sunflowers. (the scorched plants and animals would die and fertilize the soil the sunflowers would soon occupy...).

Another possible "plant" analogue might exist around a planet similar to Jupiter, with leaves that are metallized and pass through the magnetic field of the primary, generating electrical energy. You might also imagine a "plant" which uses chemosynthesis living near a hot vent under the ocean as well.

Nature will always find a way.

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We have red and blue plants right here on earth. China’s Red Sea Beach, Panjin comes to mind: http://www.grindtv.com/random/chinese-wetland-has-beachgoers-seeing-red/#gEPwaeBVU5cACojl.97

This red grass, known as sueda (seepweed) remains highly tolerant of the area’s alkaline soil. In April at the start of sueda's growth cycle, it exhibits a light red color, then turns green during summer, before maturing to the deep crimson color in September. This might suggest that green plants are better suited for the intense sunlight of summer, but that other colors may thrive in an environment with certain soil compositions and a weaker and more defuse sunlight.

But basically, it all comes down to chlorophyll. Chlorophyll absorbs red and blue light and reflects green frequencies. On early earth, microbes used another molecule called retinal, which reflects red and blue light and absorbs green. (Bacteriorhodopsin is another such molecule.) Some scientists theorize that chlorophyll evolved in latecomer lifeforms that couldn't compete with the retinal using lifeforms, and so evolved to take advantage of the frequencies of light that retinal based life ignored: http://www.livescience.com/1398-early-earth-purple-study-suggests.html

Dominant life on early Earth might have been purple with chlorophyll- and retinal-based organisms living side-by-side. Chlorophyll based life won out due to the greater efficiency of chlorophyll over retinal at utilizing its preferred wavelengths of light. One can easily imagine on some distant alien world that its flora evolved another hued molecule, due to local light wavelengths and soil conditions, which sports an even greater efficiency than chlorophyll. Black earth anybody?!?

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Zoochory.

You have to consider the rest of the life on the planet.

If you can imagine a situation that can cause your animals to ingest and disperse seeds based on colour, then plants red in colour will continue to be distributed.

Perhaps the planet has some really odd limitations around its position to its star, its chemical composition, or its geographical features. It could be such that the water and soil content (which is very red in colour) is healthy for the plant species on the planet.

This could be an initial startup for the phenotype, and it might be sufficient if the soil is such that simply everything that grows there is red in colour.

Once other organisms come along and start dispersing the plants by ingesting them and spreading their seeds, they learn that non-red plants don't have the health benefits. Maybe non-red plants are really toxic because they typically grow in hostile environments but still manage to survive.

So plants that are red in colour are spread more than those non-red plants, leading to a primary plant colour of red on the planet, where non-red is in sparse locations.

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re: sunlight — Atmosphere could affect which frequencies of light are more abundant.

re: soil — Oxidized iron is reddish (think of mars) and Bromine is reddish-brown (but is very toxic and doesn't occur much on Earth). An abundance of other elements or compounds might cause a different color.

Other factors that might influence plant color...

  • The dumb luck of evolution. (example: A pink bacteria got the first foothold on life and everything else is either bootstrapped from it, and.or it is at the bottom of the food chain.)
  • Being silicon-based instead of carbon based. (Not sure what effect this would have exactly. Everything is gray or clearish?)
  • World actually created by a mad scientist/wizard.
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