The Fungus' body consists of a spherical, beige torso with a concave tip. It is connected to the ground by five dark brown trunk-like stipes. While the lower parts of the Fungi don't move by themselves, the upper section appears to be bulging in a manner similar to breathing. Apparently posing no threat to any other creatures, Xen Fungi appear in slightly different forms, varying only in size. Xen Fungi live alone or in a group of several organisms. They can also grow on cave ceilings as seen in the Gonarch's Lair.
Xen Fungus behind Bullsquids drinking from a Healing Pool on Xen.
 List of appearances
- Half-Life: Day One (First appearance)
- Half-Life: Opposing Force
- Half-Life: Blue Shift
- Half-Life: Decay