Appendages coiled or hooked at tip - UncinulaAppendages simple and straight with bulb-like base - PhyllactiniaAppendages branching dichotomously (antler-like at tip) Cleistothecium contains a single ascus - Podosphaera Cleistothecium contains several asci - MicrosphaeraAppendages simple or irregularly branched, often entangled Cleistothecium contains a single ascus - Sphaerotheca Cleistothecium contains several asci - Erysiphe
Key to Genera of Powdery Mildew(Drawing courtesy of C.B. Kenaga, E.B. Williams, and R.J. Green)