becomes overgrown with thick vegetation in the absence of the normal fire regime that maintains open clearings. Wildfires are beneficial for this plant, because they clear the large and woody vegetation that prevent sunlight from reaching it. Despite the plant's tolerance of disturbance, populations occurring near roads and cultivated fields are vulnerable. Many populations in the Willamette Valley are threatened or already extirpated by agricultural and urban development. Over the last 150 years 99% of the wetland habitat in the Willamette Valley has been altered or destroyed. The possible future construction of a dam threatens a large population. Even in protected areas the plant is threatened by the invasion of non-native plant species. Such weeds include reed canary grass (Phalaris arundinacea). Other threats include herbicides and predation by the weevil Macrohoptus sidalceae. This checkerbloom is known to hybridize with its Sidalcea relatives, such as Sidalcea cusickii, a process that can lead to genetic pollution of the rare plant. References nelsoniana Flora of Oregon Flora of Washington (state) Endemic flora of the United States Endangered flora of the United States