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I have a planet too far away from its sun for photosynthesis to work well, so the plants use chemosynthesis. But since they don't use sunlight, would they have any reason to grow above ground? Some tall(tree sized) ones too? They need to be above ground so the herbivores have easy access to them.

And what structures would these plants have to collect whatever chemicals? This world's lifeforms use liquid methane and/or ammonia (I'm undecided on which one would be best) and hydrogen gas.

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  • $\begingroup$ just a thought but if you had gases that they needed in the air, they would grow higher to get more of it $\endgroup$
    – Topcode
    May 11 '20 at 14:58
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    $\begingroup$ @Topcode They'd grow wider, not taller. It's easier to grow wider than taller because you don't fight gravity. $\endgroup$
    – Halfthawed
    May 11 '20 at 15:01
  • $\begingroup$ @Halfthawed not always, if we assume wind is higher and less of them grow tall, the tallest would get the most $\endgroup$
    – Topcode
    May 11 '20 at 15:10
  • $\begingroup$ Do the plants themselves perform chemosynthesis, or do they use the giant tube worm strategy of housing chemoautotrophic bacteria inside them? $\endgroup$
    – HDE 226868 ♦
    May 11 '20 at 15:19
  • $\begingroup$ How do they reproduce? Growing tall doesn't have to be just to get "nutrition". Maybe the tall ones get eaten by the herbivores and their seeds/spores are carried some distance away before pooped out which allows the plant to have a larger range. Adaptations don't happen in isolation. $\endgroup$
    – ColleenV
    May 11 '20 at 15:39
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There are a lot of details needed to answer this question well, but let's take a stab. I'll guess your "plants" will look a lot like fungi & mushrooms. They are taking energy from their environment, but not the sun, and will spread along the sources of that energy. If it comes from chemicals in the soil, they will infiltrate the soil. If the chemicals collect on pools, the plants will look like pond scum. If they are in water/the ocean, the plants will take on specialized functions to harvest the chemicals from the water. The real challenge comes if you want above-ground structures to be eaten by herbivores. The lines between chemo-plants and chem-animals would be MUCH blurrier, as these organisms would be all carrying out the same functions. Plants could try to eat animals, animals could drink chemical food. These suggestions are an ecosystem - multiple strategies could all be working in different climates and chemical environments. Some plants would take advantage of primary chemicals, others of reactions subsequent. A lot depends on the sources of energy.

  • Some of your organisms will evolve scum-like life across the surface, like lichen and moss. they will infiltrate surfaces to extract chemicals, scattering as resources deplete. Animals could scoop these up off surfaces, and the plants could grow back from the "roots" like grass.
  • Fruiting bodies can carry seeds/spores further it they are scattered by (winds?) They will be modest structures compared to the vast organisms underground. To be carried by wind, they would want to be as tall as possible. Protect these from being consumed if they are tall/semi-permanent.
  • Fruiting bodies can also take advantage of herbivores as seed/spore vectors like plants do. Flowers allow pollinators to carry genetic information, and then later fruits allow the transport of seeds. Use everything plants do today (there are vast numbers for strategies; best to just look these up)
  • Complex functions of plants require space, not just at a cellular level. Competition for simple chemicals would be high, and your plants could grow "refineries" to carry out chemical reactions better carried out on scale. Imagine a plant that heats a chemical to volatilize it out of soil or rock. It's not how plants/organisms work on Earth, but hey, why not? These refineries could be filled with high-energy chemicals and would be valuable - I see them like cacti. They could use "smokestacks" to carry toxins into the air. A forest of such structures could look a lot like a real refinery. They could even have symbiotic organisms that have evolved to be "refinery workers" and either help the plant carry out functions, or defend their chosen territory while the workers only harvest minimally from their chosen species.
  • Valuable micronutrients could be carried in the air, and would require an above-ground structure to compete with other plants for this nutrient. Such collectors could look like rain-collecting structures - an organism lining a depression, or large goblet-shaped bodies. In this case, the tallest/widest structure would be the most efficient. It better be valuable, though - like food (nutrient-chemical) raining from the sky. The structures could even retract when it wasn't "raining" nutrient to protect themselves.
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Your plants are electrotrophs.

st elmos fire

https://captainjetson.com/featured/st-elmos-fire-what-you-dont-know-about-air-travel/

In your cold, dusty world, airborne dust can accumulate large amounts of electrical charge. Since your world (is it the same world?) is so cold that methane is liquid, the atmosphere is mostly hydrogen which conducts electricity even worse than ours. Huge charge differentials accumulate in the air before finally equalizing via immense lightning bolts.

Your "plants" take advantage of this by offering the charge an easy way down. Plants extend as far up as they can reach, and put out branches with many ramifying tiny spikes. The spikes glow with corona charges / a.k.a. St Elmo's Fire most of the time (as depicted above) - they are collecting the atmospheric charge and giving it a path to ground in exchange for a little work on the way. Thus your autotrophs fix chemicals in such a way that heterotrophs can eat the chemicals and take advantage of the stored electrical energy.

In dense growths the corona charges from these towering plants are enough to light your dark world.

I can feel a comment coming - yes it is from L.Dutch - and he asks how a sunless planet can have wind. That is a very good question. This rogue planet is spinning extremely rapidly and the atmosphere does not quite keep up with the planet below. High winds result. Thus the ultimate source of energy for this world is the rotational momentum of the planet itself.

crystalline electrophiles

enter image description here

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  • $\begingroup$ I was thinking giving the world a decent amount of active volcanoes would make wind happen. I never said it was a rogue planet. It's just a good ways out in its solar system. $\endgroup$
    – Chickenpeep
    May 12 '20 at 0:54
  • $\begingroup$ The electrical stuff may be a bit problematic for tall prey animals that have tall legs(keeping its main body far away from where it makes contact with the ground) in order to more easily evade predators that hunt by vibration. And can I have more info on the appearance of these plants; the parts herbivores can easily consume without killing the plant? $\endgroup$
    – Chickenpeep
    May 12 '20 at 1:01
  • $\begingroup$ Re appearance - these plans would want to maximize points, to distribute charge and not have too much at any one place. They might look like giant horsetail plants - google those. Or they might look like crystals on your cold world. I made an image; added above. $\endgroup$
    – Willk
    May 12 '20 at 14:45
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Probably not

They'll scale as needed to get resources. Your plants will generally grow sideways instead of vertically (as @Halfthawed points out in comments). On Earth there are plants that don't rely solely on photosynthesis. Mushrooms use sunlight for producing fruit, but they don't have an incentive to grow to tree height. Below is an exceptionally tall mushroom and it's still shorter than the man holding it. Despite their short stature, mushrooms can cover massive amounts of space. The "humongous fungus" has a similar surface area to the Mall of America.

Large mushroom

Plants need a reason to grow tall. If there's a lot of crowding, you could conceivably end up with plants growing vertically because there's no room to grow horizontally.

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One reason for a plant to grow tall (tall being relative) is for pollination and seed dispersal. In fact, there are plants that are sort of chemosynthetic, rather than photosynthetic.

One example is the snow plant (Sarcodes sanguinea) which grows in the US Sierra Nevada and north into the Cascades. It derives its nutrition from mycorrhizae living in the soil, which in turn are symbiotic with conifers. The plant lives most of its life underground, but in spring will push up a bright red flowering spike which later bears seeds. https://www.fs.fed.us/wildflowers/plant-of-the-week/sarcodes_sanguinea.shtml

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