Abstract
Because Eurasian samples of Neoerysiphe collected on the Asteraceae were not identical in morphology, the molecular and morphological differences among these specimens were compared with those of the American N. cumminsiana. Neoerysiphe on Asteraceae was found to consist of at least four different species. Three of them are described as new species, viz. N. hiratae, N. joerstadii, and N. nevoi. Neoerysiphe hiratae is a Japanese species parasitizing hosts belonging to the genera Cacalia and Ligularia (tribe Senecioneae). Neoerysiphe joerstadii was found in Israel on Phagnalon rupestre (tribe Gnaphalieae). Neoerysiphe nevoi was recorded in Israel and Ukraine on a number of hosts in different genera but all belonging to tribe Cichorieae. Thus, Eurasian Neoerysiphe species infecting the Asteraceae are strongly specialised to particular tribes of this family. Phylogenetic analyses indicated that the three new species were not closely allied. Neoerysiphe hiratae is related to the American N. cumminsiana and species belonging to Oidium subg. Striatoidium. Neoerysiphe nevoi is sister to N. geranii, and N. joerstadii is allied to N. galii. In addition, Ukrainian Neoerysiphe samples on Geranium were phylogenetically and morphologically identical to Japanese samples of N. geranii, and this fungus seems to be an invasive species in Ukraine.