The powdery mildews, Erysiphales, with the only family Erysiphaceae, form a large group of obligate plant parasites. Most of the mycelium exists at the outside of the plant; only in a limited number of species the plant is entered through the stomata. With small, specialised structures, appressoria, the hyphae are firmly attached to the epidermis of the plant. Precisely from these points small extensions penetrate more or less deeply into the tissue and extract nutrients.
The mycelium forms large masses of asexual conidia. Sometimes one by one, at the end of a hyphe, more often in chains. The conidia of some species characteristically contain strongly refractive particles that remind one of tiny shards of glass, the so-called fibrosin bodies; they are visible only in fresh material (e.g., in Podosphaera fugax).
Sexual reproduction occurs in generally globular, darkly pigmented structures, cleistothecia (also called chasmothecia), in which a limited number of asci is formed. Some species (almost) never make cleistothecia; species that do make them generally do so in late summer. Cleistothecia often have characteristically formed appendages.
Alexopoulos, Mims & Blackwell (1996a), Braun (1995a), Braun & Cook (2012a), Takaamatsu (2013a), Zheng (1985a).