Isatis tinctoria
Threats to this rare species include invasive species, wildfire suppression, and construction and maintenance of roads and radio towers. The non-native noxious weed dyer's woad ("Isatis tinctoria") directly competes with the mariposa lily by monopolizing water and nutrients and producing allelopathic substances which inhibit its germination. Fire suppression efforts at the California sites have resulted in overgrowth of native trees and shrubs such as Oregon-grape ("Mahonia aquifolium") and curl-leaf mountain mahogany ("Cercocarpus ledifolius"), which shade out small wildflowers such as mariposa lilies.