. . . . . . . . . "Pyrus calleryana" . . "Gymnosporangium" . . "Matthew O'Donnell. 2014. Pyrus calleryana host to parasitic fungus Gymnosporangium. iNaturalist.org. Accessed at <https://www.inaturalist.org/observations/748740> on 05 Apr 2018." . . . . "http://iNaturalist.org is a place where you can record what you see in nature, meet other nature lovers, and learn about the natural world." .