In his protologue, Boissier (1867) cited two gatherings: “in Bithynia, Thirke” and “circa Amasia et Tokat Anatoliae, Wiedem.”. Wiedemann’s gathering at G-BOIS is here chosen as lectotype. Munz (1967a) indicated that he saw a duplicate of this gathering at GH and K. However, the duplicate at GH could not be found by the curator. It is unclear whether the Wiedemann’s gathering at K of D.thirkeanum (K000075588), which is apparently a duplicate from a specimen at LE, belongs to the type material. Moreover, Huth (1895) quotes a specimen at LE, which was not observed.