<jats:title>Abstract</jats:title> <jats:p>The close genetic relationship of the mushrooms Retiboletus griseus and R. nigerrimus is supported by the occurrence of the orange-yellow retiboletic acid, resp. its methyl ester, in both species. The structures of these highly substituted pulvinic acid derivatives have been elucidated by spectroscopic investigations. R. nigerrimus also contains two N-protocatechuyl-L-phenylalaninol derivatives, nigerrimin A and B, the first reported occurrence of such compounds in nature. Their configuration was established by the synthesis of nigerrimin B