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Mint is a highly invasive plant that rapidly takes over gardens with its sprawling root systems. In my story, a group of scientists engineer a particularly prolific strain of mint in order to increase industrial yield. They have more success than they expect, and begin shipping “super mint” seedlings to farms across North America. Due to poor containment while transporting the specimens, the super mint is accidentally introduced into surrounding ecosystems. It spreads at an uncontrollable rate, crowding out much of the native vegetation, disrupting food chains, and eventually decimating native wildlife populations. By the time the scientists discover their mistake, the mint has already taken root across entire forests, and is still spreading rapidly.

Over the next 150 years or so, super mint replaces the vast majority of terrestrial plant life on Earth, causing mass extinctions, particularly in forests where tree seedlings cannot compete with the hyper-aggressive mint, leaving only endless fields of tangled, six-foot-tall super mint plants.

Is it feasible that genetically engineered mint could be aggressive enough to replace almost all life on Earth?

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    $\begingroup$ Seems like in the world your building it's not only feasible it's what has already happened. I'm not sure what you expect from us. You have mint with undefined superpowers. We'd have to know the specific capabilities of your mint to be able to discuss the feasibility, which is moot because in the world your building the answer is already known. $\endgroup$
    – sphennings
    Nov 16, 2023 at 4:13
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    $\begingroup$ Shallow roots, couldn't compete with grapevines that burrow hundreds of metres through dry soil. Unless you say it can... In which case, yeah. Could you define it a bit more, what its limitations are? Temperature limits, length of seed viability etc.. $\endgroup$ Nov 16, 2023 at 4:24
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    $\begingroup$ So like kudzu on steroids? $\endgroup$
    – Trang Oul
    Nov 16, 2023 at 8:14
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    $\begingroup$ @TrangOul looks like kudzu is instead super-mint on steroids. OP says super-mint is mere 2m high, while kudzu is 30m high and can block trees off sunlight, also kudzu spreads a lot faster and also has a nitrogen fixation symbiosis on leaves, having a positive feedback loop over itself. In fact, I'm scared of this thing ever reaching Europe, it could easily eat up everything in here over a hundred years. (And why kudzu didn't eat up the whole of China yet?) $\endgroup$
    – Vesper
    Nov 16, 2023 at 14:42
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    $\begingroup$ @Vesper In its native range, there are insects and fungus that consume the kudzu. There have been studies that are looking for things that exclusively feed on Kudzu. $\endgroup$ Nov 16, 2023 at 15:01

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It's not that reasonable.

For one, mint doesn't grow well everywhere. It needs plenty of water to thrive, meaning that dry or arid climates wouldn't be easy for it when compared to less needy plants.

Additionally, if monocultures have taught us something, is that some life forms which thrive on the thriving species will show up, keeping it under control.

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    $\begingroup$ I, for one, volunteer to drink enough Mojitos to keep this scourge at bay $\endgroup$
    – Richard
    Nov 17, 2023 at 18:48
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    $\begingroup$ @Richard You may need limes for your mojitos... and sugar cane to make the rum. $\endgroup$
    – ukrutt
    Nov 18, 2023 at 16:28
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    $\begingroup$ @ukrutt - The US govt likely have vast underground stocks of both, enough to ride out the mintpocalypse $\endgroup$
    – Richard
    Nov 18, 2023 at 16:55
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Even superplants have competition

In the real world there are plenty of examples where certain invasive plants can be considered 'superplants'. It is important to note that there's no hectares of superplants that have out competed everything in an area. Sure you can see some areas where it's a real problem, but a full blanket of mint from horizon to horizon, and the horizon beyond, and beyond that are unlikely.

The reasons are simple. Survival of the fittest. The existing plants have two advantages. The first is that they are already there, limiting soil and nutrients. They might shade an area, depriving it of vital sunlight or even the fungi in the ground might not cooperate with the mint. The mint needs to adapt to a wide range of situations, soil compositions, water requirements, sunlight, water depth, droughts. It isn't unconceivable that it can adapt to a wide range of situations, but during the adaption time it is vulnerable. Not to mention that any plant could do the same, but hasn't.

Finally such a plant would get predators at a certain time. It is abundant and has energy. Something will eat it eventually.

How to still get a 'superplant' that covers the world.

Your best bet is to not directly compete, but cheat. First of all, you make a plant that easily adapts. This increases complexity, and thus makes it harder to truly compete. But you have two extra weapons. The first is that there's many kinds of the mint created, able to cross breed easily, allowing the flexibility to reach further heights and many kinds are already prepped for many environments. This will make competition much easier.

The second is that it attacks anything that isn't one of those mint plants chemically and virally. Your plant is able to sample the plant life around it and create chemicals as well as bacteria or viruses to the detriment of other plants. Think of simply increasing the acidity of the ground by leaps and bounds. A virus might not kill another plant outright, but as it's spending so much energy to defences it is easier to compete with.

It will have a bigger chance to disrupt ecosystems, causing them to collapse. I still think it'll not cover the world, but it has a good chance to be as prominent as grass while edging out other plant life. It can still be the 'hellscape' of mint you want to be, though less prominent.

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    $\begingroup$ The idea of "creating" new bacteria and viruses is barely within the powers of human scientists; delegating it to a plant seems rather far-fetched. I like the basic idea, though, so perhaps instead you need some engineered symbiosis that causes a highly-adaptable bacterium to "want" to help the mint by killing its competitors. $\endgroup$
    – IMSoP
    Nov 16, 2023 at 10:01
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    $\begingroup$ @IMSoP I agree it is far fetched. I imagined something like a normal immune system, but adapted to create enzymes, viruses or bacteria specialised to attack the foreign plant matter sampled in the environment. Killing isn't the direct goal, but only outcompeting your enemies. Symbiosis of a highly deadly bacteria is a good idea as well. You could even do something like caterpillars that find a home in the mint and eat anything else. But a superplant is far fetched regardless, so I thought to give some ideas how to get there. $\endgroup$
    – Trioxidane
    Nov 16, 2023 at 12:55
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    $\begingroup$ Hm, I hadn't considered the immune system analogy; so these could be something like T cells, aggressively killing anything not matching the host plant's genome, and entering into adaptive arms races with the existing immune system in other plants. $\endgroup$
    – IMSoP
    Nov 16, 2023 at 13:51
  • $\begingroup$ A less far fetched plan, is that it was engineered to disperse herbicides or cross breeds with other plants that do. This is not that crazy of a thing for the plant engineers to want and many plants naturally do put off herbicides to kill other competing plants. $\endgroup$
    – Josh King
    Nov 16, 2023 at 15:20
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    $\begingroup$ The plant wouldn't need to create "new" viruses. It could come with a library of well-known viruses instead. When it detects a competitor or predator, it could then produce the appropriate virus for the fight. A lab capable of genetically engineering a tough plant, may also have access to a catalog of known viruses. $\endgroup$ Nov 16, 2023 at 15:28
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Unlikely

First, even super-mint should have some requirements to proliferate, and could only do this slowly, as plants don't make seeds more than twice per year, also while mint has rootstalks, it's still limited in spread due to them not able to extend fast enough (energy requirement, as mint is still a plant). So, even to take a single forest, one plant would take several dozen years.

Second, if some species gains abundance in a certain region, local life that feeds on such species (plants here) would have an adaptation vector to eating what's abundant, and soon would gain the ability to feed on it, leading to additional external vectors of deterrence to your super-mint's spreading. An example would be Panama disease of bananas, which are a human-spead monoculture alike your mint, this stuff hit bananas worldwide thanks to human-induced spread via spores in a matter of years, effectively eliminating that culture. The same may and eventually will happen to your super-mint, although not as devastatingly due to mint being able to generate new genome contrary to bananas.

In fact, we here have an example of such a super-plant introduced to better environment, namely Heracleum sosnowskyi being quite a pest in Russian rural regions, which proliferates quite widely but did not effectively eliminate other plant life, because it does not fare well in all environments. The same should apply to your super-mint.

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There are a few obstacles that need to be overcome (genetically or story-introduced) in order to do this.

  1. Vining-ness. Mint requires part-sun or more and grows a few feet high, so it has no way to outcompete tall vegetation that might shade it. Making it be able to grow on vines might let it cover trees like kudzu.
  2. Soil density/salinity. Mint propagates via shallow runners, so extremely dense (because of rocks or permafrost or some other reason) or oceanic terrain would effectively stop it. It needs some adaptation to overcome these. Growing on vines would help for some examples, but not all.
  3. Deep desert. While there are mints that have adapted to arid conditions, mint cannot outcompete succulents in a pure desert environment, just due to the fact that mints can't conserve water the way succulents do. I have no idea how to adapt to this without making it less effective elsewhere.

If your genetic enhancements can overcome these three barriers, there are very few environs that could avoid being overrun.

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Something like this already exists, with no genetic engineering required. It's called kudzu.

Kudzu smothering trees Kudzu smothering trees (public domain)

Kudzu smothering hill Kudzu smothering hill (© Katie Ashdown)

Could genetically engineered plants "replace almost all life on Earth" if humans didn't interfere? Yes. But realistically, major governments would be willing to spend trillions of dollars to prevent that from happening.

The only way to pull this off is to deliberately create an invasive bioweapon. Genetically engineer a sort of "green goo" or shoggoth/kudzu type organizsm, as described here:

Overview of existing natural biology:

Minimum doubling time for

  • Plants: single digit days

  • Algae: 1.5 days (ideal conditions)

  • E.Coli: 20 minutes (nutrient rich conditions)

Evolution is dumb and slow

Very simple strategies (EG:vine that climbs a tree and squeezes) are "innovative" and work well in nature.

A naive biosphere stands no chance against an intelligent opponent with real biotechnology.

Hypothetical very invasive shoggoth/kudzu type organism

Core capabilities:

  • constructed from modular components

    • does not grow a leaf, sends leaf parts via internal transport network to be assembled on site
  • dedicated networks for long distance distribution of water and high concentration sap (think honey)

    • sap is concentrated and low in phosphorus, sulfur and micronutrients, inhibits bacterial growth

      • water contains some inorganic micro-nutrients

      • sap and water can be combined inside parts to run normal biology

  • general purpose transportation system to move encapsulated blobs of stuff

    • EG: inorganic nutrients, excavated dirt/rock, matter to be digested

    • think a pneumatic tube system with lots of switches

      • maybe use water instead of air
    • containers can be re-used

  • distributed nervous system

    • all parts communicate conditions and requirements (EG:I am a leaf making sugar, send more water pls)

    • contains many simple biological computers that route messages

Core organism competency is covering ground with photosynthesising mat of itself.

edges contain assimilating parts

  • Traps for annoying animals

  • slow moving mouth parts to reduce trees/animal corpses in size for shipping to digesters

  • digesters/factories to convert trees/animals/soil into "build a giant leaf"/"build a trap"/"build an X" parts kit

    • digesters can do much better than nature by extracting and re-using existing cellular machinery

      • digesting into amino acids and rebuilding is not efficient
    • assemblers that assemble parts kits into parts to integrate with the whole

    • some parts may be mobile/dockable EG:mouth parts could travel a bit on a tether then come back

As organism scales, modularity allows for much faster growth since growth at edge only requires assembling prefab components

  • growth could easily be 100m/day spread with 1-100KM/day spreading via dedicated pipeline based "shoots" to increase linear spread speed.

    • IE: elephant sized worm like part powered by pipeline it lays down. Lays down expansion nodes every kilometer where normal growth initiates

    • can grow flying things to spread much faster, then link up with other parts of itself

This is just biochemistry and organism templating. No need to build complex brains.

tl;dr: Wiping out most life on Earth with a genetically engineered plant is feasible if no one intervenes. However, people would intervene. Making this work in the face of active resistance requires deliberate design choices.

Unless. . .

Perhaps the scientists were using an Artificial Intelligence to do their bio-engineering (Some future version of AlphaFold?)

Scenario 1: The A.I. disregards the scientists' orders and deliberately engineers the plants as a bioweapon.

Scenario 2: The A.I. designed exactly what they asked for (maximum growth rate, maximum disease and pest resistance, etc.) but was much more successful than they planned on.

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  • $\begingroup$ "But realistically, major governments would be willing to spend trillions of dollars to prevent that from happening." Yeah, about that.... $\endgroup$ Nov 17, 2023 at 7:26
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    $\begingroup$ You are correct if we are only talking about wilderness areas. I was assuming the mint would be overrunning large amounts of farmland as well. (Humans and domesticated animals make up ~90% of Earth's land mammal biomass. Not sure what percent of plant biomass our crops are, but the mint would have to wipe out a large fraction of farmland to replace "almost all life on Earth.") $\endgroup$ Nov 17, 2023 at 14:18
  • $\begingroup$ smithsonianmag.com/science-nature/… Has a useful reflection on how much kudzu is mythologised. It's invasive but not hyper-invasive It doesn't spread much outside the regions to which it is suited. It doesn't cover Wisconsin nor Mexico, since it needs a certain climate, and it is subject to attack from a range of bugs. $\endgroup$
    – James K
    Nov 18, 2023 at 8:34
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If it can handle diverse ecology then it can certainly take over up to a point and for a short time (in evolutionary terms, so could be millions of years).

Your main problem would be getting it overseas. I live on an island mid Pacific Ocean, it would be difficult for it to come here for example. So traversing geology would be a major issue to solve especially once it was a recognised problem. How will it get over the Alps, across Oceans, deserts etc,.

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  • $\begingroup$ I don't see it as that much of a problem. Plants and animals take rides on humans and human transportation all the time. Someone hikes in an area that has invasive plants and comes home and brings the seeds home on shoes or clothing. We could protect some islands, but so long as there's trucks and trains and planes running everywhere, some seeds will leak through to every major part of the world. $\endgroup$
    – prosfilaes
    Nov 17, 2023 at 4:24
  • $\begingroup$ @prosfilaes rubbish, I live on an island, we're very careful about what gets in. It's not a matter of luck, we have a whole dept on the job. $\endgroup$
    – Kilisi
    Nov 17, 2023 at 8:47
  • $\begingroup$ Yeah, you live on an island where you're very careful about what gets in. Eurasia, Africa and the Americas make up most of the world, and have minimal effective protections against things coming in, and little enough internal controls. They're not going to stop every train from Germany to Italy and scrub it and check every passenger for tiny mint seeds, so the Alps aren't even a question. $\endgroup$
    – prosfilaes
    Nov 18, 2023 at 1:21
  • $\begingroup$ @prosfilaes Perhaps not in the West because they've a bad track record, but lots of places have very robust controls and much less travel $\endgroup$
    – Kilisi
    Nov 18, 2023 at 2:07
  • $\begingroup$ The Polynesians introduced the pig, the dog and the rat all across Polynesia. One of the earliest examples of animal importing was baboons into Egypt, and places all around the world, India, Africa, South America, have imported Eucalyptus trees for planting. As for travel, there are 25 million refugees from Africa and Asia, which means a lot of people moving from one place to another with little control. $\endgroup$
    – prosfilaes
    Dec 14, 2023 at 23:32

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