Mushrooms do not contain flavonoids

•Mushrooms do not contain flavonoids.•Mushrooms cannot synthesize flavonoids since they lack required enzymes.•Fruiting bodies as well as mycelia do not absorb flavonoids from the substrates.•Unspecific colorimetric methods are mostly utilized by literature for their determination. A literature and database review and several experiments were carried out because of the perturbing increase and exponential spreading of a major mistake thought scientific publications. Up to October 2015, more than 136 reports ensured that mushrooms contain flavonoids. However, 91% of the publications used an unspecific colorimetric method that was developed to quantify them in plants. However, no sequences encoding chalcone synthase or chalcone isomerase (key enzymes involved in the flavonoid biosynthetic pathway) were found in genomic databases even in completely sequenced mushrooms indicating that they do not have the enzymes needed for their production. Fruiting bodies obtained from substrates containing onion wastes and mycelia grown on media supplemented with specific flavonoids showed no flavonoid content after HPLC DAD/MS determinations indicating that they were also unable of absorbing them.