Cultures of the causal fungus of Kikuyu Yellows disease of Pennisetum clandestinum isolated from Australia have been examined. The fungus is described. The oospore has three noteworthy features: it is plerotic even into the oogonial neck; the ooplast appears to develop a condensed core; the relative thicknesses of the oospore wall layers appear to differ from those of other Oomycetes. Oogonial characters and parasitism indicate an affinity with the graminicolous downy mildews. However, asexual sporulation is not immediately reconcilable with that of these mildews. A major re‐appraisal of the classification of the peronosporalean fungi has been necessary to accommodate this fungus. Attention has been drawn to mycelial morphology. Three new orders and two new families are recognized. The division between the peronosporalean fungi and saprolegnialean fungi is recognized at the sub‐class level.

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DICK. M. W., CROFT, B. J., MAGARF.Y, R. C, de COCK, A. W. A. M. & CLARK, G., 1989. A new genus of the Verrucalvaceae (Oomycetes). A fungus, isolated from sugar cane in Queensland, Australia and causing the Poor Root Syndrome disease, is described and shown to be related to Verrucalvus and possesses verrucate oogonia containing plerotic oospores; it is placed in the Verrucalvaceae (Sclerosporales). On the basis of morphological and DNA studies the Verrucalvaceae has to be placed in the Saprolegniomycetidae. It follows that the order Sclerosporales (and also the Leptomitales) must be removed from the Peronosporomycetidae and placed in the Saprolegniomycetidae.

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