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I'm inquiring about the possibility of plants on other worlds developing the ability to move over land on their own (they need not be sapient, but I wouldn't rule the possibility of sapience out either). At the moment two hurdles to overcome have occurred to me-

A) the need to develop an equivalent to animal muscle tissue,

B) how it could (for lack of a better word) "re-root" itself to take in water and nutrients from the soil.

Are there any solutions to these issues (and for those who accuse me of asking two questions, they are connected and basically two sides of one problem)?

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    $\begingroup$ Are you looking for a full-fledged walking flower that can go in any direction at will, or can its movement be pushed by pure chemical feedbacks (light level, humidity...)? Movement is more than muscles, you also need the command system (a.k.a nerves) to operate it. $\endgroup$ Nov 3, 2023 at 22:38
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    $\begingroup$ @Tortliena- yes, a walking plant that can go in any direction. $\endgroup$ Nov 3, 2023 at 22:56
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    $\begingroup$ Do you want to know if such plants could physically exist in the real world according to known science, or are you looking for a set of plausible-enough explanations (which also overcome your 2 hurdles) for such a form of life , such that you feel justified using the concept in your world/story? If it's the latter, I could probably take a shot at it, but if it's the former, I can only presume the answer to be: yes. $\endgroup$
    – M S
    Nov 3, 2023 at 23:08
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    $\begingroup$ I’m voting to close this question because (a) You're asking at least three questions (read your title), (b) asking if alien life can "exist" is meaningless, we have no proof (yet) whatsoever that life exists off of Earth, so asking if life can exist on an alien world must either be answered "no" or "it's your imaginary world, have it if you want it." (c) Worse, SE focuses on specific, solvable problems. Asking about "the possibility of plants..." is open-ended (*Continued*) $\endgroup$
    – JBH
    Nov 4, 2023 at 1:36
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    $\begingroup$ There won't ever be 'alien plants'. There may be things that look or act like our plants do, but they'll be less related to our plants than we are to the most unrelated lifeform on Earth. The only resemblance they'll have to plants will be just that: a resemblance. That said, mobile autotrophs are possible. $\endgroup$
    – Monty Wild
    Nov 4, 2023 at 2:45

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Yes.

Such trees exist on our planet as well.

“As the soil erodes, the tree grows new, long roots that find new and more solid ground, sometimes up to 20m,” said Vrsansky. “Then, slowly, as the roots settle in the new soil and the tree bends patiently toward the new roots, the old roots slowly lift into the air. The whole process for the tree to relocate to a new place with better sunlight and more solid ground can take a couple of years.”

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    $\begingroup$ I don't know why this was deleted, but it's too useful to remain so. $\endgroup$
    – Monty Wild
    Nov 4, 2023 at 2:42
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Frame-change:

Existing plants are just fine with movement as long as it isn't quick movement, especially movement in response to stimuli.

The classic example is plants turning to 'face' the sun over the course of the day, but this is far from the only means of doing so. They can sense gravity and move against it. Plants have a limited ability to 'choose' which way they send their underground runners based on outside criteria, they follow complex criteria in deciding when to release seeds or spores, and they can even move in response to vibration or touch.

So if you were able to work on a timescale of every movement requiring the growth of a new 'body' at its destination, it would be relatively trivial to give them movement without going beyond what plants can already do in nature. It's only when you need them to move as quickly as an animal that you'd have to come up with abilities that don't exist on Earth.

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What is the definition of "plant"?

According to Aristotle, a plant has a "vegetative soul" capable of growth, nutrition, and reproduction; whereas an animal has a "sensitive soul" capable of all the above plus perception and mobility. In other words, an animal has the ability to sense and react to its environment, and that's what makes it an animal.

If your alien organisms are able to see, hear, feel, or otherwise sense what's going on around them, and to move or act in response to that, then I think they cease to be "plants" (even if they're green or whatever). Or are you talking about something that moves in an automatic way, i.e., not in response to events but just by following the wind, the sun, or something? In that case, because it lacks "perception", it could still count as a plant, sort of.

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  • $\begingroup$ This is precisely the question I had. Without further specification, it's like asking if animals in another world could be stationary, without dedicated organs and photosynthesise. Which aspects can you change before they stop being plants according to the OP's definition. $\endgroup$
    – EdvinW
    Nov 10, 2023 at 19:46
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This all comes down to two aspects:

  1. how fast you want them to move, and
  2. in what stage of their development you want them to move.

Note that the vast majority of Earth plants already move! Almost all plants display some degree of phototaxis (growing their chlorophyll-bearing bits in the direction of sun) and hydrotropism (growing their roots in the direction of water). There are also other cues that guide growth, such as the presence of other tree crowns at the canopy layer. They're just not fast. There are good reasons for this - the energy density required is too much when balanced by the large surface area that optimises photosyntesis, and in any case they don't need to go anywhere, because their food isn't going to run away.

But also, many plants move (some quite a lot!) in their reproductive phase. Gametes (pollen) and seeds have a pretty varied range of dissemination strategies, from the passive (wind) to the passive-but-with-a-helping-hand (pollinators, berries) to the very active (exploding seed pods and the like). These are not usually photosynthetic on their own, and use the parent's resources to power their dispersal (the flesh on a fruit, or the pressurised seed pod of a violet). Your plant could have evolved a particularly fun seed dispersal mechanism.

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