A revision of Albugo (chromista, peronosporomycetes)

After a revision of the taxonomy and nomenclature of Albugo, it is concluded that this genus contains at least three groups of species that deserve generic level. Taking into account the unique features of these organisms, the subclass Albuginomycetidae and the order Albuginales are introduced. The genus Albugo is emended and two new genera, Pustula and Wilsoniana, are introduced for the white rusts of Asteridae and Caryophyllidae, respectively. Based on morphological, ultra structural and molecular grounds, eight new combinations are proposed: Pustula chardiniae, P. hydrocotyles, P. tragopogonis, Wilsoniana achyrantis, W. bliti, W. platensis, and W. portulacae.