Taxonomy and distribution of the poorly known Erysimum vassilczenkoi (≡ Syrenia macrocarpa) (Brassicaceae) is revised on the basis of herbarium material and field studies. The presence of the species in the flora of Mongolia is not confirmed; instead, a new species, E. mongolicum, is described from the Mongolian Altai, and E. kotuchovii is reported for Mongolia for the first time. The distinguishing characters and relationships of the three species are discussed. A map of their distribution and a key to their identification also including the closely related E. siliculosum are given. Some comments on the status of Syrenia are added.