Fungal Mould is a rare substance in No Man's Sky obtained via Farming Star Fungal Clusters at your Home Base or from the same plant in the wilds of Toxic Planets.
It's primary use is in the construction of Acid, Insulating Gel & the Tau Hyperdrive upgrade.
Where To Obtain
Here is a planet where Fungal Clusters grow that only requires the first 2 Portal Glyphs to dial:
It is a Low Bio-Hazard Planet with High levels of Fauna, a fair amount of which is aggresive, it's Flora is medium.