Catalyzes the reversible decarboxylation of aromatic carboxylic acids like ferulic acid, p-coumaric acid or cinnamic acid, producing the corresponding vinyl derivatives 4-vinylphenol, 4-vinylguaiacol, and styrene, respectively, which play the role of aroma metabolites. (E)-4-coumarate + H(+) = 4-hydroxystyrene + CO2 (E)-cinnamate + H(+) = CO2 + styrene (E)-ferulate + H(+) = 2-methoxy-4-vinylphenol + CO2 Binds 1 prenylated FMN (prenyl-FMN) per subunit. Homodimer. May form higher order oligomers. Belongs to the UbiD family. UbiD-like/FDC subfamily.