Is there other things than trees that contain cellulose and lignin?

Yes, cellulose and lignin are found in various plant materials beyond trees. Many herbaceous plants, including grasses and shrubs, contain cellulose in their cell walls, while lignin is present in smaller amounts. Additionally, agricultural residues like straw and corn stalks, as well as certain fungi and some algae, also contain these compounds. These materials contribute to the overall biomass and can be utilized in various applications, including biofuels and biocomposites.