The aim of this study was to examine in detail all previously described species of Hemileia which were available as herbarium specimens. Morphological characters were observed by means of light- and electron microscopical methods. The value of the observed features for the division of Hemileia from other rust genera, the circumscription of the genus and the differentiation of single species were extensively discussed. The present work includes detailed information about the history and taxonomy of the genus, as well as a list of host species together with keys to the Hemileia species which parasitise them. The individual species were described, illustrated and discussed. Doubtful, unclear and excluded species were also listed and discussed. One new species was described: Uredo kilimanjarensis. The following new combinations and names were introduced: Hemileia castellanii, Hemileia cumminsii, Hemileia detergibile, Hemileia sydowiorum, Hemileia wakefieldii, Uredo evansii, Uredo harunganae and Uredo jahnii.weiterlesen