The player can break off the "Mushroom Cap" of Tree Mushrooms to obtain Fungal Samples, by hitting them with the Knife or by direct collision with the Seamoth or Cyclops, causing them to break and slowly drift to the ground. One "Mushroom Cap" yields about 2 to 14 Fungal Samples, depending on the size. The only practical use for Fungal Samples is fuel for the Bioreactor.
Fungal Samples are not scannable.
Uses In Crafting
Spoiler alert: The following section contains story related material.