Family of homologous FMN-dependent alpha-hydroxyacid oxidizing enzymes. This family occurs in both prokaryotes and eukaryotes. Members of this family include flavocytochrome b2 (FCB2), glycolate oxidase (GOX), lactate monooxygenase (LMO), mandelate dehydrogenase (MDH), and long chain hydroxyacid oxidase (LCHAO). In green plants, glycolate oxidase is one of the key enzymes in photorespiration where it oxidizes glycolate to glyoxylate. LMO catalyzes the oxidation of L-lactate to acetate and carbon dioxide. MDH oxidizes (S)-mandelate to phenylglyoxalate. It is an enzyme in the mandelate pathway that occurs in several strains of Pseudomonas which converts (R)-mandelate to benzoate.