Natural phenols can be involved in allelopathic interactions, for example in soil or in water. Juglone is an example of such a molecule inhibiting the growth of other plant species around walnut trees.  The aquatic vascular plant Myriophyllum spicatum produces ellagic, gallic and pyrogallic acids and (+)-catechin, allelopathic phenolic compounds inhibiting the growth of blue-green alga Microcystis aeruginosa.
Phenolics, and in particular flavonoids and isoflavonoids, may be involved in endomycorrhizae formation.
Acetosyringone has been best known for its involvement in plant-pathogen recognition, especially its role as a signal attracting and transforming unique, oncogenic bacteria in genus Agrobacterium.  The virA gene on the Ti plasmid in the genome of Agrobacterium tumefaciens and Agrobacterium rhizogenes is used by these soil bacteria to infect plants, via its encoding for a receptor for acetosyringone and other phenolic phytochemicals exuded by plant wounds. This compound also allows higher transformation efficiency in plants, in A. tumefaciens mediated transformation procedures, and so is of importance in plant biotechnology.