Intimate ecological interactions occur among plants, fungi and bacteria. Mycorrhizal fungi live within special root compartments co-created with plant partners and they are symbionts with over 90 percent of living plants today. Fungi help make many valuable nutrients available to plants. The plants provide sugars to the fungi.
Symbiosis generates the high diversity and vast biomass of terrestrial life. All organisms consist primarily of water, and interact easily in fluid habitats. The evolution in land biota of the intimate association of networks of cells (through which fluids and solids are transported) are already well established in the Devonian Period.