Mycelium
Fungi, one of the most important parts of a healthy soil life, next to billions of microorganisms of course. They break down organic material, toxic substances and even plastic. They improve the condition of the soil and help plants to grow at a better capacity.
In a forest, the underground mycorrhizal network connects all the trees over which they share water, nutrients and they even use this so called “Wood Wide Web” to communicate with each other, I.e., sending signals about diseases, droughts and pests. In return, the fungi get a part of the sugar that the trees photosynthesize from sunlight which means they live in symbiotic relationship.
The largest known fungus has been found in the Blue Mountains in Oregon btw and it spreads over about 965 hectares or roughly 1’665 football fields which makes it the biggest organism living on planet Earth.