Lignin doesn't neatly fit into a single functional group. It's a complex polymer made up of aromatic alcohols.

Here's why:

* Aromatic: Lignin is primarily composed of phenylpropane units, which have a benzene ring, making it aromatic.

* Alcohol: The phenylpropane units contain hydroxyl (-OH) groups, characteristic of alcohols.

However, lignin also features other functional groups, including:

* Ethers: The monomers are linked by ether bridges.

* Carbonyl: Some lignin components contain carbonyl groups (C=O).

Therefore, while lignin has a strong aromatic and alcohol character, it's not strictly classified under a single functional group.