Sawadaea bicornis
Sawadaea bicornis is a species of powdery mildew in the family Erysiphaceae. It is found across the world, where it affects maples.
Description
The fungus forms thin, white irregular patches on the leaves of its host. Sawadaea bicornis affects many species in the genus Acer, including Acer macrophyllum, A. campestre, A. pseudoplatanus, A. negundo, A. grandidentatum, A. tataricum, A. circinatum, A. saccharinum, and A. platanoides. Some of these species can also be affected by Sawadaea tulasnei so care should be taken to distinguish the two.
Taxonomy
The fungus has two different formae. S. bicornis f. bicornis affects Acer campestre and A. planatoides. S. bicornis f. polyphaga is a more virulent form that has evolved to infect a much larger range of host species and is introduced across the world.