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What is a quasi-creature plant?

I define a quasi-creature plant as an organism that lives only through photosynthesis that moves with a speed in the same order of magnitude of that of an animal.

Here on Earth, almost nothing

On Earth almost all plants move very slowly, orders of magnitude more slowly than animals. It is because the low energy provided by the Sun does not allow waste of movement.

What kind of potential environments would be good fits?

In what kind of situations, if any, would a plant moving with a speed in the same order of magnitude of that of an animal be possible? Maybe orbiting around a blue star, more light would get to the surface, or a binary system with the right timing could make the planet almost night-less, doubling the energy available for photosynthesis.

Is it more probable to be in air, water or ground?

Ground

Even something like a plant with a huge green surface over itself that stays still most of the time, but when there are no predators (read: herbivores) it moves using tiny legs hidden underneath to get more sun?

Water

Maybe as water is where the life started this would easiest with a creature spending most time in the dark fondal but raising to near the surface where few predators are nearby.

Air

Or a flying(?!) plant with a huge membrane that gives it great aerodynamics and at the same time takes much sun, it would swing the wings very slowly not to end up its energy and rest atop trees when there is not enough sun?

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  • $\begingroup$ If you had a large planet that spun quickly, it could be closer to the sun and receive more insolence, pushing the photosynthesis calculation further into the black. Rather than morning glories and sun flowers, we'd start to see sun walkers. What about symbiosis? A creature covered in moss that provides more energy, physical protection, more oxygen with plant respiration exhaling into the lungs? I actually had created a DnD race based upon this concept... $\endgroup$ – Isaac Kotlicky Jun 19 '15 at 11:23
  • $\begingroup$ Earth knows moving creatures that live off photosynthesis: en.wikipedia.org/wiki/Volvox $\endgroup$ – Mnementh Jun 19 '15 at 17:35
  • $\begingroup$ There is an animal that kind of generates energy like a plant the green sea slug (en.wikipedia.org/wiki/Elysia_chlorotica) eats algae and then can use parts of the algae to generate energy from the sun. but that makes it more of a quasi plant creature rather than the way you want it $\endgroup$ – SilverShadow Oct 24 '17 at 22:28
  • $\begingroup$ adding to @Mnementh there are a lot of fast moving plants and there are some fast growing plants, too. And then it depends to which animal you compare it. I want to add that all plants are creatures. You may think too "fast animal"-centric here. $\endgroup$ – Henning M. Oct 25 '17 at 22:39
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Sorry, but this is extremely unlikely.

For a steady flow of energy like sunlight, it is more efficient to cover as much of the surface that receives sunlight as possible. For this the keys are ability to spread your seed widely and to sustain periods unfavorable conditions. A plant that moved around to catch sunlight would find itself blocked by trees that have been growing at the spot it wants to go for years. You could make a plant that climbs trees to catch light, but I don't think there is anyway that could be energy efficient and out-compete plants that simply wait for the light.

Same with nutrients, growing roots or waiting for insects to be trapped is more efficient than searching for nutrients by moving around.

The basic problem here is that since photosynthesis requires no movement from the plant, the ability to move would be inefficient. It is possible to imagine circumstance where moving would be useful, but very difficult to imagine any there it would be the best option.

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It's not just having enough sunlight. It takes a lot of energy to move. Some types of Bamboo can grow over 100ft. in 3 months. there are in areas where growing conditions are optimal, Lots of sun and plenty of rain, and a rich enough soil.

The much bigger question, why would a plant that gets what it needs, sun, water and dirt for nutrients even have a biological need to move? We move partly because we need to collect food to continue living. I know plenty of people that if they could live by sitting in a pile of dirt with a little sun light would put a sun room in their living room and a garden bed in front of the TV.

Currently our plants use all of their energy to grow larger (to collect more sun, food and water) and/or to produce seed to spread their kind.

A slightly more plausible creature, would be an animal that has photosynthesis as a secondary means of collecting energy. Maybe as a symbiotic relationship like lichen. Or just a way to help deal with a scorching sun in the desert, a lizard uses photosynthesis to collect energy during the day to be more active at night...

Edit: Actually a predator that does its hunting by waiting could find the photosynthesis to be a boon. It could wait for very long times in between prey walking by to capture and eat, basically being on 'stand-by' mode, with a trickle charge keeping everything running.

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  • $\begingroup$ Doubtful that an animal could profit from photosynthesis. Randall Munroe of XKCD has made the calculation for a green cow, and it only is worth 4% of energy intake: what-if.xkcd.com/17 $\endgroup$ – Mnementh Jun 19 '15 at 17:34
  • $\begingroup$ @Mnementh I didn't think it likely, but I do think it's more likely than a plant wondering around. $\endgroup$ – bowlturner Jun 19 '15 at 17:36
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The issue isn't the amount of sunlight that is received on Earth, but rather the relative inefficiency of photosynthesis. On Earth, we receive 1366 W/m2, which is enough to make solar cells and solar thermal energy viable for rooftop installations on a person's house to provide electricity and hot water. Of course the average PV cell is @ 20% efficient in converting solar radiation into electrical energy (low cost cells are much less efficient, the theoretical efficiency of a single layer PV cell is @ 33%).

Plants, on the other hand, have a conversion efficiency of about 3-6% of the incoming solar energy, and lacking active cooling mechanisms, would have difficulty in raising that efficiency. This is most evident in agriculture, where it takes @ 1 acre of land to feed one person for a year. (Obviously this changes depending on what crops you use, the method of farming and where you are on Earth, but this can be considered an average for "normal" agricultural practice). Since plants have evolved many ways to broadcast pollen and seeds (including domesticating insects, animals and humans to serve their needs ;-) they don't need to evolve mobility; if the wind and currents don't do the job, then animal life can be coopted through the use of tasty fruit and other incentives.

High energy quasi-creature plants would have to evolve a much better means of converting sunlight to energy (perhaps using solar energy to convert chemicals into battery fluids and having organic electro chemical batteries as their power source). As well, they will need some sort of active or passive cooling system that can deal with the much higher waste heat of this process. Finally, their ecology would be very strange, with crowds of plants following the sun either East-West or North South as the seasons progressed. There would be predator/prey, parasitical and symbiotic relationships developed over the ages; "plants" which concentrated chemicals for their battery systems would be preyed upon by "carnivorous" plants with less solar gathering surface and a proboscis like feeding organ to tap the accumulated battery fluid; while parasitical plants might not have "leaves" any more, but live within the host drinking battery fluid.

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Most people agree that photo synthesis could not propel a human like creature at the same magnitude of speed. So lets make it different.

It is either an air or water based creature. It uses the natural currents involved in these fluids to maneuver itself at speeds that at times can exceed human movement by several magnitudes. The plant creatures move ruder or sail like appendages very slightly to help control their movement.

Many Earth plants already move daily to face towards the sun. Similar small actions could be used to tighten the edge of a sail sack, that catches the current or changes buoyancy.

For air I think you would need a planet with a thicker atmosphere, or perhaps a gas giant?

Evolutionary need? If this is a thicker atmosphere for a planet, perhaps less light gets through. Higher altitudes means less atmospheric blockage of light and more energy. Higher altitudes allows for greater dispersal of seeds and more opportunities for pollination.

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    $\begingroup$ The problem with air is getting nutrients. Catching birds seems unlikely; they are too fast and smart. The skyplant would have to land from time to time, maybe at night, to feed, and then rise up again in some way. That will cost a lot of energy. $\endgroup$ – Sinthorion Jun 26 '18 at 11:16
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As you said, the more photosynthesis would be available, the more your creature should develop without trouble.

So I would say before all, a planet with a low (but not null) magnetic field should help. If your plant-like develop a strong resistance to ultraviolet, x rays and gamma rays, it could transform it in energy as it do for light, and strongly improve this energy source.

For the living environment itself, it has to begin by water, and then maybe move to ground or air, as it have to start by a mono cellular organism and then evolve to a quasi-creature plant.

Once again, if your objective is photosynthesis efficiency, you can choose between air (far from every potential shadow source), ground (as efficient as air if in an empty terrain, like desert or grassland), but very shallow water is not to exclude, as it can be as lighted as ground when directly expose to sun.

But this option would limit your creature zone to shallow coasts. So if you want to expand as much as possible, ground would be a better start, and air could be better or worse, depending of quantity of flying and non-flying herbivores there is in your scenario.

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In a world where multicellular life has not evolved yet, like Earth in most of its history, eucaryotes with chloroplasts might be otherwise no different than those without, as chloroplasts came from endosymbiosis of procaryotes initially. It could be a life event, not a heritable characteristic: ingesting and digesting smaller and/or dead cells for energy as well as raw material, but capable of keeping (not digesting) a photosynthetic cell or several over time. It no longer needs to ingest sugar or burn ingested fats and protiens for energy, once it incorporates the organelles.

How much motion does the advanced cell employ, in either case? It might have cilla or flagellum, but mostly goes with the current.

More generally, the economy of scale levels the energy requirements, as does being in an environment where purposful movement is supplimentary to outside-imposed motion (whether the creature is plankton itself, or is anchored and lets food come to, it).

Even after multi-cellular life came into being, there was no "hunting" until more development. Animals were filter feeders or some passive manner; the energy budget of an "animal" would not be high.

But for a world where this persists? It seems natural for creatures to specialize as it gets beyond the filter-feeder/worm step. Plants have huge surface areas (leaves), and animals get fast circulatory systems.


I think of a similar state of affairs in hydrothermal vent tube worms, which host symbiotic bacteria that use chemosyntesis (rather than photosynthesis) and has no digestive system or ability to move other than moving it's crown in and out of its tube.

The small specialized motion (into protected shelter, deployed into environment) is rapid unlike a plant, and what you have in mind. It can easily be a critical advantage, to avoid preditors or cope with shifts in the immediate conditions (e.g. too hot or the wrong chemicals present) very rapidly.

The worms don't get up and move to another spot. They rely on a motil stage during reproduction to re-deploy in a new spot.

For your creature, suppose gossamer photo-collecting surfaces are deployed but must be adjusted rapidly depending on conditions, or reeled in ASAP if conditions become bad or preditors arrive. That uses animal muscle speeds and reaction times, as a critical component of a photosynthetic apparatus.

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There are tumbleweed plants. They get blown around by the wind, but the main structure is dead, since the purpose is to disperse seeds. It's just not worth the energy maintaining living tissue for rolling around.

There are seaweed mats that just spend their life floating around on the ocean currents. It might be possible for something to evolve the intelligence of a jellyfish - they don't have brains but just some basic light receptors that activate muscles to keep in the shadow.

Dandelion seeds are designed to be blown away by the wind. The problem with trying to float in the air is the presence of humidity and below zero temperatures which would change the weight/density ratio.

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Imagine a floating land mass in the ocean with large waves. The waves are big enough to flip over pieces of land. Individual pieces of land will always be above water, but the part of them that is above changes. If there is a reason to avoid being underwater (like predators) then it might be reasonable to move very quickly to get back into the sunlight.

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