The fungus forms thin, white irregular patches on the leaves of its
host.
Erysiphe aesculi-sylvaticae, like most Erysiphaceae, is highly host-specific and infects only two species of
Aesculus. The species on other
Aesculus, which has been introduced to Europe and Asia, is
Erysiphe flexuosa. The species on
Aesculus flava likely represents another undescribed species. == Taxonomy ==