Recently published phylogenetic analyses of the Golovinomyces orontii complex revealed that three different species of the genus Golovinomyces may occur on cucurbitaceous hosts, viz., G. bolayi, G. orontii s. str., and G. tabaci. Owing to its morphological characteristics, Erysiphe cucurbitacearum (≡ G. cucurbitacearum) was tentatively reduced to synonym with G. tabaci. However, final conclusions on the identity and status of E. cucurbitacearum, described from China on Cucumis sativus, as putative synonym of G. tabaci required a phylogenetic confirmation and epitypification with ex-epitype sequences. Therefore, a sample of G. cucurbitacearum collected on C. sativus in Xinjiang Uygur Autonomous Region, China, in 2014 (HMJAU-PM91862) has been sequenced and is designated as epitype of the latter species, since its holotype material (HMAS 40016, collected in 1954) turned out to be too old for molecular examinations. As a result of morphological examinations and phylogenetic analyses based on ex-epitype ITS and 28S rDNA sequences, the recently assumed synonymy of G. cucurbitacearum, found on C. sativus in China, with G. tabaci could be confirmed. In addition, two new host species of G. tabaci, viz., Trigonotis peduncularis (Boraginaceae) and Rubia cordifolia (Rubiaceae), were concurrently identified. Trigonotis peduncularis is the first verified boraginaceous host for G. tabaci.