These species are plant pathogens and the genus is one that causes downy mildews. Peronospora is very common and is an obligate parasite (obligate parasites cannot grow on non living environmental surfaces) found on leaves, stems, flowers, and fruits of living higher plants. Peronospora sp. may be identified in air on spore trap samples since spores have a distinctive morphology. The spores may also be seen in dust as part of the normal influx of outdoor microbial particles. As of this writing, allergenicity has not been studied and no information is available regarding health effects or toxicity.