I am currently working on a setting which is fantasy but based around a soft approach to speculative biology.

It is a tidally locked world with the habitable region based around the terminator between the bright hot sun side and the freezing dark, filled with terran descended flora/fauna. The main continent is bisected by a long range of extremely tall volcanic mountains. The south, where sunlight is more plentiful, is relatively similar to terran plant life. But the north, where it goes from twilight to darkness, is where things become much more alien.

One of the ecosystems I want to use are forests of fungal plants in place of trees, located near the ocean in a vague analogue to Europe. My biology isn't the best but I know fungi feed off dead matter.

My question isn't if it could work, but rather how it could work. I was thinking an underground system of dead matter running off into the ocean that the fungi reach down to consume. Also possible there are lots of megafauna which migrate across the continent to pass away in these area, feeding the forest as they decompose.

This setting is fantasy so 100% plausibility isn't necessary (think Dougal Dixon or Flight of Dragons).

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    $\begingroup$ There is no such thing as a "fungal plant"; fungi are more closely related to animals than to plants. And the mushrooms are the fruiting bodies of (certain kinds of) fungi; they are analogous to the flowers of plants, that is, they are temporary structures with reproductive functions. And where does the dead matter come from? $\endgroup$
    – AlexP
    Oct 15, 2017 at 23:38
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    $\begingroup$ Im thinking dead matter comes from migrating megafauna that migrate into the area at the end of their lives. Also was thinking of having flows of dead matter from streams passing from other side of the continent, accumulating dead plant/animal matter as they flow toward the ocean. $\endgroup$ Oct 15, 2017 at 23:52
  • $\begingroup$ For the dead matter issue, aside from animals (and their waste) that get trapped in the fungal forest, what about fungi (B) that feeds on dead fungi (A)? So it becomes cyclical, A dies after sporing and B feeds on the dead A, B dies after sporing and A (or C) feeds on the dead B $\endgroup$
    – n_b
    Oct 18, 2017 at 18:32

11 Answers 11


Before vascular land plants, there were weird fungal “trees.” People still do not really understand what exactly they were or what they ate. They were called prototaxites.

prototaxite forest from pinimg.com

Wikpedia: Prototaxites

Prototaxites is a genus of terrestrial fossil organisms dating from the Late Silurian until the Late Devonian periods, approximately 420 to 370 million years ago. Prototaxites formed large trunk-like structures up to 1 metre (3 ft) wide, reaching 8 metres (26 ft) in height, made up of interwoven tubes around 50 micrometres (0.0020 in) in diameter. Whilst traditionally very difficult to assign to an extant group of organisms, current opinion suggests a fungal placement for the genus. Recent discovery of what are likely algal symbionts makes it a lichen, rather than a fungus in the strict sense.

from livescience.com: Prehistoric Mystery Organism a Humongous Fungus

On the inside, Prototaxites is clearly not a plant, composed as it is of interwoven tubes just five to 50 microns across (50 microns is about half the width of a human hair). “With that anatomy, it suggests lichens, fungi or algae,” Boyce told LiveScience.

I like the idea that a lot of dead junk had built up for a fungus to eat. Certainly a lot of dead junk did build up, as evidenced by the huge coal deposits laid down during these eras. But why would a fungus need to be so freaking tall? Mysteries, mysteries. In any case: your fungal forest.

Image: Prototaxite bland fungi this image is beautiful. Not exactly a forest, but prototaxites, eurypterids and an amazing vibe.

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    $\begingroup$ Dude. How do I know about stromatolites and not prototaxites. Those are awesome. Lichens are my fave organism. $\endgroup$
    – SFWriter
    Oct 16, 2017 at 0:16
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    $\begingroup$ That is an awesome pic, did not realize we had these at one point. Thanks for the responses, i've learned quite a bit just posting this question. $\endgroup$ Oct 16, 2017 at 1:15
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    $\begingroup$ "Hey, is this weird thing possible?" "Why yes, it even happened on earth" $\endgroup$
    – MechMK1
    Oct 16, 2017 at 15:56
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    $\begingroup$ @Chad : Trees are tall to get to the light, not the oxygen. (Trees need very little oxygen at all - none during the day, they produce their own.) I also suspect that the oxygen concentration will not be that varied - turbulence will break oxygen down to ground level. $\endgroup$ Oct 17, 2017 at 11:02
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    $\begingroup$ @Chad I believe MartinBonner is correct. If anything there is less oxygen available, the greater your altitude. This is why you need oxygen to climb Everest, and some athletes train at higher altitudes to push their aerobic fitness harder. $\endgroup$ Oct 17, 2017 at 13:46

Trees are tall because they are competing for sunlight. A fungus that received all the nutrients it need at or below ground level would have very little reason to grow taller. But you want a forrest of fungi which requires tall branching structures. Fortunately there is a solution that fits your world and also solves the food source problem. Filter feeding. A tidally locked world is going to have massive continuous weather systems these storms would justifiably pick up vast quantities of organic matter, your fungi forrest could be situated at an eddy in this storm where the organic matter collects and settles back to the ground. There would be evolutionary pressure to catch this falling detritus first leading to tall branching canopies of fungi.

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    $\begingroup$ This could lead to marching forests. If the wind direction is constant, fungi in front would be able to catch more, thus spread more. Fungi in the back would have fewer nutrients and eventually die. Speed would be likely quite slow, but could lead to some interesting story points $\endgroup$
    – Lope
    Oct 16, 2017 at 8:57
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    $\begingroup$ "would have very little reason to grow taller" - the taller it grows the farther away it can spread it spores. The farther away its spores land the less competition it will be between themselves and them and parent as well as potentially spreading wider. $\endgroup$ Oct 16, 2017 at 16:52
  • $\begingroup$ @Maciej Piechotka, I meant to address this in my answer, but forgot. Yes spore dispersal is a reason to grow taller, but generally this is done with fragile impermanent stalks, and explosive spore dispersal, compared to sturdier tree like structures that would be more resource intensive. $\endgroup$
    – Lex
    Oct 17, 2017 at 17:29
  • $\begingroup$ @Lex "A lichen is a composite organism that emerges from algae or cyanobacteria living among the filaments (hyphae) of two fungi in a mutually beneficial symbiotic relationship. The fungi benefit from the carbohydrates produced by the algae or cyanobacteria via photosynthesis." $\endgroup$ Oct 19, 2017 at 12:58
  • $\begingroup$ @CeesTimmerman I know what a lichen is, but the question concerns a region with insufficient light for plant life to thrive, so lichen aren't really relevant. $\endgroup$
    – Lex
    Oct 20, 2017 at 2:44

Think of lichens.

Lichens are a symbiotic form of life, fungi and algae. Trees grow high to reach the sunlight. Fungi don't need that. But algae does. Lichens today are rather small, growing on trees, great rocks or walls. But if there are no trees or walls, they have an evolutionary reason to grow up like plants or trees.

Algae don't grow large or form hard structures, but fungi can, if they need to. The lichen can grow high as a fungi to support its algae with sunlight. Lichens can form great and fantastic structures, quite well fitting in a fantasy world.

The fungi supports the algae with water from the deep, the algae support the fungi with sugar from photosynthesis.

You would not need dead waste as a food source, but you can do that additionally. Dead waste (from elsewhere or from dead or ill lichens, too) would rather be eaten by normal fungi instead of lichens. They would add another bizarre componente in this "wood".

enter image description here

(Picture taken from https://de.wikipedia.org/wiki/Flechte)

I am thinking about a plausible reason why there could be a region where normal trees and plants can hardly survive, but lichens and fungi can. Maybe some sort of disease affecting normal plants, but algae are protected by the fungi.

Maybe more plausible is an ozone hole depressing regular plants, but surviveable by lichens. That could add some story elements as the region would have dangerous UV light for people during the day.

At night, lichens and fungi could spend some surreal bioluminescent glowing light.

enter image description here

(Picture taken from https://en.wikipedia.org/wiki/List_of_bioluminescent_fungus_species)

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    $\begingroup$ "I am thinking about a plausible reason why there could be a region where normal trees and plants can hardly survive, but lichens and fungi can" I just wanted a setting that is much more alien than the south, since this area is closer to the nightside, its in perpetual twilight, lit by the bio luminescent fungi/lichen. $\endgroup$ Oct 16, 2017 at 14:15
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    $\begingroup$ @mental_maelstorm Perpetual twilight is another premise, ok. Maybe the light is to weak to feed normal plants. But the lichen can form cups covered inside with a silvery shimmering slime, reflecting and collecting the rare light in their center to allow photosynthesis. That may be one big cup or many small cups, depending on the species. $\endgroup$
    – mviereck
    Oct 16, 2017 at 16:36

One thought that comes to mind is this: imagine that the planet isn't quite fully tidally locked but instead rotates very slowly.* Therefore on one side of the planet the Sun is always setting, but so slowly it hardly moves over a human lifetime, and on the other side it's rising. On the setting side there are (or once were) lush forests of normal Earth-like trees. Eventually the Sun goes down and those trees are cast into darkness, which kills them due to lack of photosynthesis --- but before they can fully decay they become encased in ice, where they remain for (let's say) hundreds of thousands of years as they pass around the dark side of the planet.

Your civilisation lives on the opposite side of the planet, where the Sun is rising. Those dead trees, encased in ice for thousands of years, are now nearing the sunlit side once again. It's still dark where they are, but warm air currents from the sunlit side have begun to melt the ice. Thus, the ground is covered in freshly uncovered and well-preserved dead plant matter, the perfect environment for fungi to grow. It's cold, so they grow slowly. (Otherwise they would just use it all up too quickly to reach any appreciable size.) Since there is always new dead forest emerging from the ice the ecosystem is stable and many species, including the giant mushrooms, have evolved to fit this unusual niche.

*Full disclosure: this might not matter if you're not worried about 100% plausibility, and I'm not 100% sure about the following anyway, but this situation might be quite difficult to achieve from an orbital mechanics point of view. When a planet becomes tidally locked it probably doesn't just rotate more and more slowly but instead starts rocking from side to side like a pendulum until it comes to a stop. However, it might be possible to achieve a very slowly rotating planet if it's influenced by the gravity of another body, such as a small or distant moon, or a second sun/brown dwarf/black hole etc.

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    $\begingroup$ That is a really neat concept, an extremely slow rotation which will cause changes and migrations for the lifeforms and even civilizations eventually. There could be ruins of abandoned cities locked in the ice as people migrated to safer areas. $\endgroup$ Oct 16, 2017 at 14:25
  • $\begingroup$ I love the concept of the very slowly rotating planet - I even based a FATE game setting on this idea once. While twilight zones are also fun, the prospect of the night side creeping ever closer to whatever you may have built gives the whole situation much more interesting dynamics. $\endgroup$
    – Sty
    Oct 18, 2017 at 9:12

Since fungi are not autotrophs, you need a food source. Maybe the forest is at a crucial pass and massive armies regularly battle over the spot. Thousands of casualties every month give food to the 'forest'. A passerby will see countless bodies with fungal tendrils growing into them. Old armor is half buried amidst the floor. Your fungi might even trap animals passing through the area to digest them as well, making the place hazardous to traverse alone.

Second possibility. You have a city whose waste is managed by a small fungal forest. The sewage flows out of the city to a nearby bog and piles up there. Fungi of increasing heights have begun to grow among this bog, decomposing the refuse.


Yes a "fungal forest" is very possible.

In fact, it is believed to have happen on Earth in the distant past. Before trees evolved there was grasses and among them large fungus. Some over 20ft high.

As to what they feed on, well, I think you are on the right path with fauna, mega or otherwise. There would also be spots with vegetation, bushes on higher ground. The leaves falling from them to the lower land can also provide a little "food". It is all very possible.


The reason fungi on our world use respiration to decompose detritus (and consume oxygen) is because of the endosymbiosis of the ancestor of mitochondria.

The reason for respiration among all eukarya, is down to the mitochondrion, which we all share. That ancestral bacterium dictated the use of oxygen. This made the algae and plants happy, because now their waste (oxygen) does not build up.

Your solution is simple. Create a different organelle, a different endosymbiotic event. You already have a different planet. If the event endosymbiosed a bacterium that uses nitrate instead of O2, or sulphate, etc. for its respiration, then the substrate can be different too.

In particular, if the original endosymbiotic event included a bacterium that uses fluorine for respiration instead of oxygen, (this has other problems but is an interesting exercise) then metabolism of additional carbon sources (including CO2) becomes possible.


Fungi need detritus to consume, hece you have them - on earth - as a part of forest ecosystems. Some fungi are specialised in organic matter that few other beings can decompose, like wood. Some even make peroxide, a powerful bleach!

So your question turns IMO into "How can I have a steady supply of organic material into an are where little other life survives. The answers of Vincent and Nathaniel go into that direction.

Here's my proposal: On a tidally locked planet, we'd expect a lot evaporation on the sunny side and lots of precipitation on the dark side. So most rivers will flow from dark to light. Now, if a river somehow accumulates lots of organic matter and is then - through a trick of geography - forced to meander into the twilight or dark zone, you could have your fungal biome. Plants won't thrive due to lack of light, but funghi could tap into the organic reach stream. If you want the fungi biome to look like a forest, have the stream underground, slowly seeping through a thick layerof gravel. The ground will be thick with mycelium, while the fungi push their fruiting bodies ever higher.

Now, we need a source of organic matter that's steady over a few millenia. I suggest that our river, before meandering back into the dark, flows through a sunny part of your world and gathers lots of plant matter. Maybe your fungi biome grows on the outflow of a large moor.

For this convenient flow pattern, we need a sicle shaped mountain range, paralell to the terminator (day-night line) with the belly pointing towards the sunny sides an the points to dark side. This will serve as a watershed our river has to flow around. Maybe there's the rim of a huge crater that was broken at a few convenient places? Or during an iceage, the glaciers on the dark side pushe a lot of ground towards the sunny side, creating a system of end moraines that now constricts flow.

Incidentally, the Münchner Schotterebene is a bed of gravel that was pushed off the alps over several glacials, in some parts the groundwater table is 40m below the surface. So there is a precedent for low groundwater table near heavily glaciated areas!
It gets better: the ground level falls to the north, away from the alps and the wholething finishes into a series of end morains, also there are a few moors in the north. The basic layout you need is not totally implausible!

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    $\begingroup$ Really like this idea. I am thinking that the mountain range which divides the continent has a lot of plant/animal life growing along its lower slopes, due to the geothermal heat still present, the glaciers at the top flow northward, carrying the dead matter into the twilight lands to feed these fungal biomes. I'm thinking lichen covered steppes in the west and tall mushrooms in the east toward the coast. Possibly having matter dumped in from storms that frequent the eastern ocean. $\endgroup$ Oct 17, 2017 at 1:14

You could have the a filter web made of, giant, Hyphae, basically a fungal root system covering the outlet of a stream or an ocean inlet, downstream from an elephant or whale graveyard. The hyphae feed on the effluvia flushed from the graveyard with every rain or tide and take up nutrients to feed the fruiting bodies that break above high-tie mark. The resemblance to a deep forest could be quite marked, with the hyphae forming trunk analogues festooned with seaweed and other detritus like the lichens seen in many forest and swamp biomes. As an inter-tidal environment the fungi could mesh relatively smoothly with land bound forest or mangrove swamp inviting the unwary to stumble into range of the incoming tide without ever realising their danger. From above you would see a canopy of mushroom/toadstool fruiting bodies extended up into the wind to spread spores to other feeding grounds wherever the wind blows.


When the dinosaurs died, many forests could have perished for 15 - 20 years in a row, so there would have been many tons of forests which had lots of mushrooms, millions of flies and beetles feeding of the giant dead animals for 10 years, lots of squirrels and other animals feeding from funghi and beetles.

If you had a forest that had a dark period every 2-3 years when one of the moons eclipses the sun or a super volcano erupted regularly, there could be forests that have major diebacks every few years and that become mushroom worlds for 1-2 years at a time, until the warmth and sun re-appears. any kind of cool cataclismic event that darkens the skies and provides lots of biomass would make mushroom forests.

any carbon rich source for example tar and oil volcanoes could cause giant mushrooms to have an advantage over trees. perhaps tsunamis wash away the forests every N years and make a mountain of wood someplace. mushrooms don't generate cellulose that's why they are not big.


How about if there were subterranean bodies of water supporting ecosystems of chemosynthetic life. The fungi could be growing down into these bodies of nutrient rich water or their outflows. Perhaps variations in the ecosystems would also cause variations in the fungi that grow or how they grow, thus giving regional variation to the "forest"?

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    $\begingroup$ Welcome to the site, Blake! Feel free to take the tour to get a better understanding of the site. You also get a special Internet award for doing so! $\endgroup$
    – Frostfyre
    Oct 18, 2017 at 11:51
  • $\begingroup$ I like that idea quite a bit, allows for ecosystems in lower light areas and even possibly underground. $\endgroup$ Oct 18, 2017 at 21:30

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