is the largest genus of powdery mildews (PMs), a group of obligate plant pathogenic fungi. Exploration of biodiversity generally relies on regional surveys and our aim is to investigate the PMs in Taiwan. Collections of the fungi on five plant species around agricultural environments were subjected to morphological and molecular characterization, using both internal transcribed spacer (ITS) and β-tubulin gene (TUB2
) regions for the phylogenetic analyses. Erysipheipomoeae
comb. nov., a species able to infect Ipomoea obscura
and I. aquatica
demonstrated by pathogenicity tests, has been neotypified. The two buckwheat species, Fagopyrum esculentum
and F. tataricum
, are found to be hosts of E.
. These results suggest that hosts in some plant families can be infected by more than one Erysiphe
pathogen, e.g., Convolvulaceae by E. ipomoeae
and E. convolvuli
and Polygonaceae by E. polygoni
, respectively. In addition, phylogenetic analyses of PMs on Cardiospermum halicacabum
and tomato belonging to the E. aquilegiae
complex are allocated under E. neolycopersici
comb. nov. This extends the potential host range of E. aquilegiae
complex to the plant family Sapindaceae. We conclude that awareness of the host associations of PMs can potentially benefit crop disease management.