Fluorescent Fungus is a resource that was introduced to Genshin Impact in update 2.2. It can only be found on one island in the Inazuma region, Tsurumi Island. This is the southernmost island in the game.
Fluorescent Fungus is not sold in any shop, so players will be unable to purchase it in batches, which makes farming for the resource extremely important.
There are a total of 67 Fluorescent Fungus spawn points on the map, all shown in the image above. They will take two days to respawn after they have been harvested, and they do not require any special elemental interaction for harvesting.
The Fluorescent Fungus can be found in batches all over the island but is heavily concentrated in both the north and the south. It is currently used as an ascension material for Thoma.
It is good to pick this every time you see it, especially as Thoma is not available in the game yet. You need a total of 170 of the plants to get Thoma to Level 80, and can easily have all this farmed by the time his banner appears.
We assume that future characters will also require some Fluorescent Fungus for their ascensions, so make sure you stay harvesting the resource even after you have enough for Thoma.