Thermo Fungi - ROM, 16/Nov/05


After an idea developed with John Dallman.

These fill a large hole in the ecology of the Underdark, and other subterranean places far from the energies of the sun. Deep underground fungi are often seen to be the obvious replacements for plants, but, the standard ones can only feed on organic material, so they depend on more material coming, ultimately, from the surface.

However, there exist a class of bacteria called thermolytic bacteria, which can get the energy they need to live from differences of heat, as plants get their energies from sunlight. Bacteria are single cell organisms, but you could have fungi with similar properties, referred to as 'Thermo Fungi'; thermo-synthetic rather than photo-synthetic.

Thermo Fungi live off differences in temperature, and their mycelium (mats of strands) can spread out great distances, many miles, to hot places deep in the earth, and to cooler places, maybe nearer the surface, or underground rivers or lakes. They can leach some of the elements that they need for life from out of rocks, but decaying organic material is also a useful source.

While they prefer a slightly moist environment they can pump water through their bodies from elsewhere, possibly over many miles. They do not like even indirect sunlight, which burns and dries them up in a matter of hours, and rarely does any part of them get any closer than fifty feet to the surface. However, their spores are not harmed by sunlight, until they have started to sprout.

There is often little evidence that these fungi are around, except for their fine thread-like mycelium running through cracks below the exposed surface of the rocks. Where possible these fungi use existing cracks, but given enough time they can make their own way through the hardest of rocks, though this will rarely affect the structural strength of the rock.

Mushrooms, which are the fruiting bodies of Thermo Fungi, may occasionally appear in cool dark places, deep below the ground. These are edible and have a wide range of pleasant tastes, and some (10%) even confer an Infravision ability, if made a regular part of a creature's diet.

Being eaten allows the spores of the fungi to be distributed quite widely, in the droppings of creatures; they pass unharmed through the digestion of almost all creatures. Though, the circumstances allowing them to grow naturally are quite uncommon, i.e. a good supply of organic matter to feed the new-grown fungus, while it reaches out mycelium to at least two places of sufficiently different temperature; a nearby volcanic vent, and a cool underground river would be ideal. Thermo Fungus that cannot establish itself does not reach any significant size, and typically dies after at most a few tens of years.

Thermo Fungi can form the base of an ecology, as, like plants, they can make new living material from (in their case thermal) energy, and non-living elements. As long as the core of the fungus is not damaged it may live for thousands of years.

They use a short-range irritant liquid spray (a clear liquid - hydrogen peroxide, about 50% (the other 50% is water)), made by breaking down carbon dioxide, or if necessary extracted from rocks. The spray does 2D4 damage, to all within 5', save vs. poison for half damage. This is a defence mechanism against things eating their core structure (their peripheral parts are far less well protected, and their mushrooms not at all), though they balance this with atmospheric nitrogen, to prevent oxygen concentrations so high that their structure would spontaneously ignite. This spray breaks down to produce just oxygen and water. In this way, as their metabolisms continuously produce peroxide, and it breaks down, the oxygen leaks into their surroundings, and they form an important source of fresh air, deep within the ground.

Conversely, if fire is damaging them, they will attempt to smother it with nitrogen, which often reduces the level of oxygen below that which will sustain the fire. They do this by using stored nitrogen, which their metabolism also processes, to make nitrates for them. They are not that efficient as extinguishers, and a quickly established fire, or one which has it's own oxidising agents, like greek fire or smoke powder, is more than they can handle.

Thermo Fungi are not sentient, are immobile, and their only offensive ability is their irritant spray, or using nitrogen to reduce the level of oxygen near their core, which is quite effective in killing, or driving off, most things which breathe air, from other fungi, bacteria, burrowing animals, and most larger things. Xorn and other creatures, such as some of elemental earth, that need not breathe cannot be affected. Those who carry fire near the core of Thermo Fungi, in the form of torches or lanterns, may find them extinguished, as they themselves have difficulty breathing. Only persistent creatures that will not retreat to where they can breathe properly tend to be in any real danger.

The best antidote to their spray is to dilute it with plenty of water. Some creatures collect the spray, which they use as a bleach, when diluted as a disinfectant, and when diluted even more as a mild antiseptic. There are many alchemical applications, but it can be difficult and dangerous to transport the concentrated form, except in special, very clean, containers; sudden fires often result.

Some Drow farm Thermo Fungi, and carefully feed small growths with organic material, while directing their mycelium to sources of heat and cold. They 'prune' the outer parts, once the fungi has grown big enough that this will not harm it, and compost this to feed more specialised fungi, which form the basis of their diet, or provide fodder for food or other animals. If drow and other intelligent underground dwellers know of the presence of wild Thermo Fungi in their area, and understand something of the fungi's nature, they will often do their best to defend it, in particular from death.

Deep Dryads

Some rare 'wild' Thermo Fungi, large and at least hundreds of years old, may become the homes for dryads. These 'Deep Dryads' resemble elves, though their ability to change their skin and hair colour, to the varied colours that mushrooms and toadstools take, allows them to look like either drow or surface elves, if they wish. They can similarly change the colour of their clothes, which can resemble anything from simple gowns to the complex leathery structures of some fungus.

Unlike normal dryads, who live in trees, and can freely move through plant material, these dryads can freely move through earth, though solid rock with no cracks in it slows them down greatly. The immense size of their fungi means that they may appear to be able to move more freely than surface dryads, but they cannot actually move any further away from it. They have a Speak to Fungi ability, rather than a Speak to Plants ability, and Infravision in line-of-sight. They don't like, though with a bit of practice can tolerate, direct sunlight, if the highest extensions of their fungi go close enough to the surface for them to experience this.

Otherwise they are very similar to dryads, with the same Charm and Dimension Door abilities, a similar range of languages, and a detailed knowledge of their subterranean surroundings. In particular they know of all the properties of all the species of fungi found in their area. They usually lack the skills to refine or purify fungi, and are thus limited to using the properties that are available in the raw form.

Drow who know what these dryads are tend to treat them with a certain respect, and some hint that they are, in some way, secret lesser servants of their goddess - and the fact that the dryads wont discuss this just confirms it. This relationship has led to the dryads on occasion being equipped with drow adamantite daggers, and even drow hand crossbows, with sleep venom darts, for self defence. The occasional drow male (with 16+ CHAR) may disappear into the fungus with a dryad, on a temporary or long term basis. Other humanoid creatures that might be acceptable, such as elves, half elves and humans, are rarely encountered by these dryads.

Spelljamming Fungi

Many centuries ago, an almost unknown group of drow researchers, who had become envious of the elven plant ships, completed their researches on fungus ships. This was very difficult, as the Thermo Fungus that they started from quickly withered and died, even in indirect sunlight, but they managed to breed a variety with a dark brown, almost black, pigmented protective layer.

The drow fungus ships take the shape of a large disc, one nearly featureless side of which is facing towards the sun, and absorbs heat from it. The back side of the disc, which radiates heat off into space, is where the drow have their living quarters. Part of the disc is pulverised stone, mixed with organic material like loam, and all of the disc is threaded through with the mycelium of the fungus.

Embedded in the disc are many lumps of ice, which the fungus keeps frozen by pumping heat away from them, and act as the water stores for the whole ship. The drow store meat and other perishable food stuffs near the ice, wrapped so that the fungus does not consume them. This is their food store, along with other fungi they grow on the dark side of the disc, and with water from the ice, and the air that the fungus renews, they can stay in space indefinitely. Unlike the Thermo Fungus that they culture below ground, they do not harvest the material of the ship, as this upsets it.

These ships can come in a number of sizes, but as the fungus continues to grow, it may exceed the capacity of the Helm, and the ship may need to be split up. The fungus feeds by slowly digesting the embedded rock and organic material, and uses the energy gained by the difference in temperature between the sunward and spaceward faces of the disc. Every so often it may be necessary to feed the ship another small asteroid, which it will wrap itself around, growing mycelium into the surface over a period of days or weeks, so as to detach fragments that it can leach nutrients from during subsequent voyages. Bodies of large space beasts also make a suitable food source for the ship.

Drow fungus ships are capable of very long voyages, but their structure is such that they cannot enter the gravity field of all but the smallest planet, as they would just fall apart. These ships are very slightly more intelligent, or at least reactive, than their underground dwelling relatives, and defend all parts of themselves from injury, not just their cores. If the ships are destroyed then spores drift off in all directions, but there is very little chance of any of these germinating in space. The spores need to germinate in a significant amount of organic matter to grow successfully.

Trained drow sailors can navigate the narrow passageways inside the ship disc, and may even stimulate the ship to open and close man-sized pores on either face of the disc. The drow at the Helm can see all around the disc, even the sun side, though drow dislike for sunlight tends to mean they normally put little of their attention there.

If it has considerable reserves of organic material then a fungus ship can spend periods of several days out of sunlight, while continuing to refresh the air around it. But it will not be happy to do this for more than a maximum of a couple of weeks, after which it will become dormant, ceasing to refresh the air, or cooling it's ice, and after a couple of months, start to die. After two years away from sunlight it will be completely dead, just a loosely held together floating mass, with a few viable spores.

Optional rules

Some DMs may wish there be a good reason why fungus ships are not too common. A significant suggestion is given here, below. If the ships don't have this problem, then the drow designers managed to make the on-board water into an effective extinguisher system, and these ships are no more vulnerable to fire than any others.

What the Drow don't like to talk about is the vulnerability of their fungus ships to fire. The ships are quite safe, as long as their outer protective layer (which is chitin) is not pierced by any large holes. If fire is set to these holes, the ship will start to burn, though smaller fires will be extinguished by the ship venting nitrogen near the fire to put it out. A significant sized Fireball (8 dice or more) used on a holed ship will cause a massive explosion (double the fireball dice), which includes boiling water and steam. One reason not many people have reported this is that the explosion is large enough to reach the standard maximum casting range of a Fireball spell. The hotly flaming debris flung in all directions also have an excellent chance of igniting any other flammable material nearby, like other ships.

Some Drow spell casters may attempt to use fire suppression spells to protect their ships, or even Pyrotechnics, no matter how much of a hazard the generated smoke is to them. They even have a special 3rd level spell, Suppress Fireball, the only effect of which is to remove the caster's level plus two dice of damage from a Fireball, if it is cast nearly simultaneously with one.

Variant Ships

There are several ways in which there could be variant fungus ships. Standard existing ships could be mimicked by the fungus, which has eaten all their structure (likely taking several months), and replaced it with a chitinous shell. Even things like rigging and sails might be mimicked. What might be suspicious is the way that these ships always keep the same position relative to the sun, so they have a dark side and an illuminated side, and their (brown, near black) colour is likely to be different to many original ship colours. Drow on board will be placed to stay away from the sun.

Shell ships are where fungus has been set to burrow into an asteroid, and carved away all but a thin shell no more than inches thick. This is likely to take several years, and in the process will likely produce a new fungus ship, as so much material will need to be consumed. Due to the rock interfering with the fungus absorbing and radiating heat, shell ships are likely to be considerably larger than fungus ships, to increase their surface area, and the fungus will be a layer over the inside of the asteroid shell, rather than filling it, so there will be enough energy to feed it. The void in the centre can provide living space for a lot of Drow.

Even if the asteroid had flaws, cracks and pits, the fungus can patch these with chitin, but this may be visible if the asteroid is carefully inspected. On the other hand, cracks and pits might be engineered, to allow more access ports. If it is desired to move something large into or out of the shell, this is likely to be through (concealed) access ways, around the 'middle' of the asteroid. Count the part pointing towards the sun as one pole, the part pointing space-wards the other pole, and the middle would be roughly the equator. Such access ports will not have fungus between them and the central void, as it will have been grown to avoid them.


(c) Rory O. McLean, 1980 - Jan. 2006
    Permission granted to use for non-profit making purposes