Although Eutypa lata is the main agent of Eutypa dieback of grapevine, another species of Eutypa has been isolated from diseased grapevines in Northern California. Stromata of this recently discovered Eutypa were also collected from Acer macrophyllum, A. negundo, and Fraxinus latifolia in the vicinity of vineyards, and appeared commonly on Umbellularia californica in some mixed-evergreen forests of Napa and Sonoma counties. This second species of Eutypa was distinguished from E. lata because of the sulcate ostiole of the perithecium and smaller ascospores. A morphological comparison with type specimens revealed identical features between the Californian isolates and E. leptoplaca sensu Rappaz (1987). This identification was confirmed through phylogenetic analyses of Eutypa spp. based on the complete sequence of the internal transcribed spacer (ITS) of the rDNA and partial sequence of the β-tubulin gene. These analyses also separated collections of E. maura, E. sparsa, E. lejoplaca, E. tetragona, E. leptoplaca and E. lata, confirming the previously proposed species concepts. The pathogenicity of E. leptoplaca on grapevine was established using isolates collected from Vitis vinifera, U. californica, and A. macrophyllum. The importance of E. leptoplaca in relation to Eutypa dieback and its role as a necrotrophic pathogen are discussed.