The poorly known siphonous green algal genus Pseudoderbesia was originally described from the Caribbean coast of Colombia, and the Canary Islands. Here we describe a collection of Pseudoderbesia from Rhodes, Greece, representing the first report of the genus since its original description in 1991. Cultured plants of Pseudoderbesia were characterized by upright, regularly dichotomously branched siphons, developing from long stolonoid siphons. Molecular phylogenetic analysis based on rbcL and tufA sequences confirmed the placement of Pseudoderbesia in the family Bryopsidaceae, and shows a sister relationship with Bryopsis. Although this is the first record of Pseudoderbesia from the Mediterranean Sea, it is possible that the genus is more widespread and has previously been confused with morphologically similar, but unrelated taxa, such as Pseudochlorodesmis furcellata, or that it has been erroneously attributed to juvenile stages of larger bryopsidalean algae.