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My moon is about twice the size of Earth, and orbits its planet from far away. It has no sun as it orbits a rogue planet, however its planet stretches it due to tidal heating, and thus it has heat. There is also geothermal heating. There is also a lot of rain.

Anyway, onto the plants. What would plantlife's "seasons" be like without seasons? When would they bloom, when would they fruit, etc. Would it differ between plants? Would it differ between groups of plants? Would plants constantly seed? I assume that the plants would be cemo/thermosynthetic due to lack of sunlight.

I can add more detail if needed.

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  • $\begingroup$ Hello user81612, thanks for joining us on Worldbuilding. Please note for future reference that you should ask only one question and keep your questions as focused as possible. Answering this question even on behalf of groups of plants would be an enormous task. Generally speaking, asking for a single type of plant will give you a better (more detailed) answer and solve most of the "what about the rest?" problems. If you need additional information beyond that, it would be appropriate to ask more questions (rather than try to get the whole data dump in one!). Cheers! $\endgroup$ Dec 31 '20 at 6:45
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First of all, I agree with Jdonlop's answer on the level that there will not be any surface life on a rogue planet because anything on the surface would be a subarctic wasteland with liquid or gaseous water only ever existing very temporarily following major eruptions. This water just could not exist long enough for life to evolve there.

That said you may still get something that sort of resembles seasons based on the formation and death of hydrothermal vents. While some of these vents last as long as 10,000 years, many last much less than that. The life cycle of vents can vary a lot though based on how deep underwater they are, how much pressure is built up in the magma chamber feeding it, and how quickly your plate tectonics are drifting apart.

In general, your plant like organisms would colonize the chimneys of hydrothermal vents where the water is cool enough for macroscopic organisms to survive, but still putting out enough chemicals to feed them. Your organisms will slowly bloom and become more numerous the taller the chimney becomes as thermally survivable surface area increases. Eventually, the chimney would either fall over or simply lose pressure killing off any life that is there

There is no guarantee that you organisms will flower and fruit at all since strictly speaking, they are not really "plants"; so, I would personally expect a life cycle more similar to coral polyps, but if you choose to make them flower and fruit it could be related to their ability to "feel out" the impending death of their vent. As the chimney gets too tall, it will become more seismically unstable letting the plants on it know it's time to colonize. At this point they could flower and fruit so that "fish" or whatever motile organisms you choose to consume your fruit can consume the seeds and carry them to other nearby vents where their excreations can deposit them.

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  • $\begingroup$ +1 on the note that these organisms would not be recognizably "plants", since they would not need, among other things, leaves. $\endgroup$
    – jdunlop
    Dec 30 '20 at 21:17
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There Would Be No Seasons

Seasons are dependent on the availability of energy (sunlight). If your plants are chemo/thermosynthetic (and thermosynthesis is speculated as being feasible only for unicellular life), they will not have any "growing season", they'd just grow, presumably slowly.

I find it implausible that there would be rain, however. Tidal heating produces additional geothermal heat, not atmospheric heat, so if the liquid of life on this planet is water, you'd presumably have a global icecap and liquid oceans beneath it.

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  • $\begingroup$ Good point on the rain part... I'll have to figure that out, lol. However, what I basically meant was, "When would plants bloom, when would they fruit, etc." Here, I'll change it. $\endgroup$
    – user81612
    Dec 30 '20 at 20:09

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