Oxyfern

Oxyfern is a plant that converts carbon dioxide into oxygen, making it a renewable early-game source of breathable gas when grown in a carbon dioxide-rich area. It has no growth cycle, but it does have environmental requirements: it grows in temperatures from 0 °C to 40 °C, needs gas pressure between 25 g and 10 kg, and requires a carbon dioxide atmosphere. Domestic Oxyferns can be planted in a Planter Box, Farm Tile, or Hydroponic Farm.

When domesticated, an Oxyfern consumes 19 kg of water and 4 kg of dirt per cycle, while producing 18,780 g of oxygen and consuming 375 g of carbon dioxide per cycle. Wild Oxyferns operate at one-quarter the rate of domesticated ones, producing 4,680 g of oxygen and consuming 93.78 g of carbon dioxide per cycle, but they require no water or dirt. In practice, a domesticated Oxyfern converts about 98% of its water input into oxygen, which is slightly more water-efficient than an Electrolyzer, though it also adds the dirt cost.

Their gas conversion rate is close to a Duplicant’s breathing rate, but not exact enough to match cleanly one plant per duplicant. A domesticated Oxyfern produces about 31.3 g/s of oxygen and consumes about 625 mg/s of carbon dioxide, so roughly 3.2 domesticated Oxyferns are needed to offset one duplicant. This near match can still lead to either oxygen surplus or carbon dioxide buildup if the farm size is not managed carefully.

Oxyferns also have a very high pressure tolerance and multiply the mass of their input gas by 50, which means small amounts of carbon dioxide can become large amounts of oxygen. This makes them useful for turning concentrated carbon dioxide into breathable air, but it also means they can overpressure surrounding areas if the output is not dispersed. Because their pressure range is higher than that of oxygen diffusers, standard gas vents, and even Electrolyzers, gas production elsewhere may stop first if the local pressure rises too much. In a base with good gas circulation, this usually prevents Oxyferns from overpressurizing on their own as long as they are not producing more oxygen than is being consumed.

If Oxyferns are kept in a sealed room, their high conversion ratio becomes especially important. A sealed farm starting with carbon dioxide can eventually fill itself with oxygen and then stop growing once the room pressure rises too high. For a sealed setup, the safest upper limit is a very low carbon dioxide pressure if continuous operation is desired, since the plants must still have room to grow while their output accumulates. Such arrangements can eliminate the need to vent oxygen into the base, but they require active pumping of carbon dioxide in and oxygen out.

Because they convert gas at their own body temperature, Oxyferns can also contribute to heat management. If kept cool and supplied with very hot carbon dioxide, they can delete a meaningful amount of heat while producing cold oxygen. Their cooling effect is modest compared with specialized temperature-control plants, but it is still useful when paired with hot carbon dioxide sources.

Oxyfern Seed is sometimes offered in a Care Package. Outside of that, there is no normal way to increase the number of Oxyferns on the map without exploiting seed splitting.