I am looking for a chemical reaction which can generate a lot of Gas in a short period of time, on the order of seconds, to build up pressure and allow a plant to propel a seed like projectile.

The main limitation is that the reaction should be plausible from a natural evolution perspective. For instance, Potassium + Water is not plausible because how would it evolve ? This is not a rhetorical question but rather a "Vibes" based one. Of course you could construct a plant which naturally evolved the ability to make C4, or any other compound. But even if in World it naturally evolved no reader would say "Yeah, this checks out". So i am looking for a reaction that isnt obviously a product of my, or i guess your, idea but could be seen as something that naturally evolved.

In addition, it would be good if the reaction was a repurposed trait. So say two chemicals a plant could feasibly already have, which were simply repurposed for this goal. Since this is something evolution likes to do.

Whilst the plant(s) in this context have undergone evolution on an exoplanet, since this is something that has not evolved on Earth it is ok to just consider this question in the context of Earth biology. I can take it from there and we all get spared a lot of extra unneeded context.

I have done a bit of googling into this, to check the few reactions i knew from memory. Most dont appear plausible. For example, Acetic Acid + Sodium bicarbonate. Both of these are fairly simple compounds and Acetic acid could presumably be part of another chemical process inside a plant. But Sodium Bicarbonate ? Idk... Other stuff, like Ammonium Nitrate + Water seems questionable from the NH4NO3 side.

So yeah, i hope i explained by issue adequately. Thanks for reading !

EDIT; Additional Context upon request

A core concept of the Exoplanets evolution are BPNs, Biochemical Pulse Networks. A BPN, loosely speaking, is a large collection of networked Plants, here called Lignicolae, which can communicate with each other and are organized in a hierarchical system.

Some Plants, Intrinsic Members, are responsible for processing information and controlling the collective, redistributing resources etc. Generative Members are responsible for making Energy, Perceptive Members collect information and so on. Note, these niches are generated by AED (Artificial Ecological Drift). The idea is that the BPN will apply new selective pressures which steer evolution. Say we have two plants, both of which can detect Sunlight and transmit this information to the BPN. But one, through random mutations, does it a little bit better. The BPN can understand this difference and will allocate more resources to the slightly mutated and for its purpose better, plant. Which intern applies a new selective pressure, as for this species it suddenly becomes valuable to develop better Vision. Because better Vision means more energy from the BPN. This is AED in a nutshell and it has resulted in stuff like this; enter image description here

On the left you have a Teptelit, and on the right a Talantal. Both are Perceptive members which through AED has vastly over exaggerated sensory structures. The Teptelit has a enormous Compound eye, whilst the Talantal can hear and generate sounds.

With this basic setup, this question is about Protective members, which fall into a few classes. The one i am struggling with are those which launch projectiles.

What they have to overcome is a Frontline. Opposing BPNs will intoxicate the bordering soil and build Fortification structures. So "No-Mans land" can be 100s of meters wide. Additionally, the Frontline between two BPNs is almost always deprived of resources maybe one or two kilometers inwards and entirely supported by resource streams coming from deeper within the Forest. As such, the plants in question would have to launch their projectiles at least a few 100 meters. They also need to be fast enough to dig themselves into the ground upon impact and deliver a heavy ish payload.

What the payload does depends on the species. The example species i am working on would launch a package that aims to disrupt operations on the other side. So imagine a big seed that gets fired to the other side, quickly connects itself to the supply lines and causes havoc by sending in biochemical stimuli to confuse the BPN. But this is just one possible specialization. Another will be launching seeds to the other side to establish a bridgehead. So we are talking about maybe a few kg on the high end over a few 100 meters.

As for why this is more practical than having birds do it. There are two reasons. BPNs have very tight control over anything directly connected to them. They can, through for example Talantals, communicate with Animals, but that is less precise. There are many cases where BPNs will use Animals for their advantage. For instance there are Protective members which grow across the Frontline and are protected by small insect like creatures. So this is a thing, its just that there are multiple ways of doing the same thing. The 2nd reason is resource related. Opposing BPNs do have ways of dealing with intruding Animals, and are not really Afraid of going scorched earth. Any intrusion / Push is a multi decade long process and it is, over the long term, more sustainable to have static attack vectors. But again, this stuff is still used.

I hope this cleared stuff up xD

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    $\begingroup$ Maybe give a bit more detail on the performance you're expecting? in the real world, "explosive dehiscence" is a splendidly named thing, and there's stuff like the dynamite tree can accelerate seeds to 70m/s with ranges up to 100m (but generally less). What do you want your trees to be able to do? what weight? what range? (and maybe why its better than being tasty and getting birds to transport stuff further than you can throw?) $\endgroup$ Oct 6, 2023 at 16:01
  • $\begingroup$ @StarfishPrime , i made an edit, hope it clears up your questions $\endgroup$
    – ErikHall
    Oct 6, 2023 at 16:30
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    $\begingroup$ Does it need to be a gas-propelled projectile? You might look at the squirting cucumber for inspiration, either with the payload being ejected as with the cucumber, or with the cucumber-equivalent itself being the payload, propelled like a water rocket. $\endgroup$ Oct 6, 2023 at 17:46
  • $\begingroup$ @ChristopherJamesHuff Thanks for the tip ! It does not have to be gas propelled. I just focused on that as an example, i should have made that clearer $\endgroup$
    – ErikHall
    Oct 6, 2023 at 17:51
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    $\begingroup$ The oak tree outside my window is shooting acorns all over the place. Here is some explanation of the process. dof.virginia.gov/far-flung-seeds Here is a story of police being called because a tree was shooting at people. mcalesternews.com/news/local_news/… $\endgroup$
    – David R
    Oct 7, 2023 at 15:05

2 Answers 2


Let's start with what does this in nature. Kinda

There's two organisms we can take examples from.

  1. The bombadier beetle - hydroquinone and hydrogen peroxide is stored in two separate chambers, and combined to form a scalding, noxious spray from their rear. Hydrogen peroxide formation is interesting, because, well, it's a component of rocket fuel. It even, with the right catalyst and in high concentration, can be a rocket fuel on its own. And biology loves a catalyst

  2. Bamboo - does not do the chemistry needed, but forms a long, straight, mostly hollow tube

So, let's mash some components together. First off - the barrel. Though we're essentially going to be making rocket fuel, we need something to shoot with. I'd propose a structural mutation in bamboo, that makes it a double walled structure, with an inner and an outer ring. The space in the middle is left empty, and the space between the inner and outer ring keep the same nodes as before - these are more densely packed, however, giving some extra strength to the barrel, and have some important structures in them.

This is, obviously, going to be a one shot weapon. But that's fine. Bamboo grows fast.

Next up, hydrogen peroxide. Well, ok, we don't need a beetle. Plants already produce hydrogen peroxide, it turns out its a waste product from photosynthesis. I'd propose the bamboo secretes it into the inner ring as a kind of waste dump. Might be a little unlikely, but, hey, this is probably more directed evolution. Several pumps recover water from this dump, leaving concentrated H2O2.

The central tube isn't open to the air. It has several large seeds growing in it. These have a soft fruit, full of catalytic enzymes for hydrogen peroxide.

Once the first seed is ripe, some sort of signalling cascade kicks off. The first seed is released, and falls down the barrel, until it reaches a narrower point and jams. The unripe seeds fall into the hydrogen peroxide below. The rapid catalysis of H202 -> H2O + O2 creates heat. At a critical point, the remaining hydrogen peroxide starts to boil, filling the tube with an explosive, rapidly heating mixture. Eventually, the runaway reaction gets hot enough, The mix of gasses explodes, with an extra kick from, essentially, the walls of the plant burning in near pure oxygen. Your seed shoots out, burning, at an unpredictable angle. The explosion of the bamboo scatters burning fragments around, which ignite other rocket bamboos, causing a mass artillery barrage, and burning down pretty much anything around it.

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    $\begingroup$ I love it. I was hesitant to use barrels before but the idea of using a bamboo like structure is genius. It grows fast, and is as such disposable. Which is what you want, as many barrels as possible in as short of a time as possible. This is probably exactly what i need, ill wait a few hours to see if there are other answers. But thank you a lot ! $\endgroup$
    – ErikHall
    Oct 7, 2023 at 9:44
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    $\begingroup$ Thanks! Fair warning, this exists firmly in the "theoretically possible" biology space - like, yes, things create hydrogen peroxide, and yes, bamboo is straight and forms nice barrels, but this is probably going to blow up the plant. $\endgroup$
    – lupe
    Oct 7, 2023 at 23:20
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    $\begingroup$ However, I might keep all the chemistry the same, but locate it in a long, spiky, mangrove like seed, with a hydrogen peroxide filled lower chamber - rather than a long barrel taking the force, it could ignite and burn slowly, like a rocket. I'm kind of seeing a cluster of seeds, like a multi barrelled rocket launcher. $\endgroup$
    – lupe
    Oct 7, 2023 at 23:24
  • $\begingroup$ i understand, of course all of this is highly speculative since there really isnt a good point of reference on Earth. But it feels plausible enough, given over 100 million years of evolution took place $\endgroup$
    – ErikHall
    Oct 8, 2023 at 8:44

Base it off of the Sandbox Tree

Sandbox trees (sometimes called dynamite trees for an obvious reason) have fruit that explodes projecting its seeds out at speeds of ~70m/s. That is about the same projectile speed as a particularly well made medieval warbow. The actual explosive part of this fruit is pretty potent, but not very well directed. It would not be unreasonable to assume that some distant cousin of these trees might one day mutate to have bigger, longer, harder fruits designs to fire out in a more ballistic trajectory.

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    $\begingroup$ Something like this, with the barrel idea from lupe, could probably work. Ideally you would want some control over the direction it goes and i have some ideas. So thanks for this as well ! $\endgroup$
    – ErikHall
    Oct 7, 2023 at 9:45

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