In this laboratory exercise, learners will discover how many different plant hosts they can find that are infected by the same genus of a powdery mildew fungus, or how many different genera of powdery mildew fungi can be found on the same plant host. This exercise demonstrates the diversity that exists within a fungal order. With a good collection of leaves infected with different powdery mildew fungi (collected by learners or instructor), learners use a written key and/or an illustrated key (or could even make their own key) to identify the powdery mildew fungus to genus. Since powdery mildew fungi reproduce by means of two spore types, asexual spores (conidia) and sexual spores (ascospores), discussions of the types of reproduction in fungi can be facilitated. Note: This lab works best in regions that experience cold weather for part of the year, since this encourages production of cleistothecia (sexual stage).