A fungus characterised by the absence of cross-walls in the mycelium and, when sexual reproduction occurs, it produces an oospore, and it does not involve an ascus or a basidium. The most important plant pathogenic Phycomycetes are the Peronosporales (downy mildews). Phyllactinia
A genus of the powdery mildews in which the cleistothecia contain many asci, and the rigid appendages lift the cleistothecia from the leaf so that they fall to the ground. Phyllotaxis
The arrangement of leaves on a stem. This arrangement may involve opposite pairs, whorls, alternates, etc.
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