The Brayton-Horsley Prairie is a 14-hectare prairie and spring fen complex in Bremer County, east-central Iowa. Three community types are found at this site, including mesic prairie, wet prairie, and spring fen. Of the 192 native vascular plant species found at this site, 35 are considered rare within the Iowan Erosional Surface. Nine are considered endangered or threatened in the state in the 1986 publication of Roosa et al. The spring fen community was found to harbor most of these rare taxa. Fens are one of the most important habitats in eastern Iowa for rare plant and animal populations, and should be protected to help preserve regional biodiversity.