Bloodroots (Sanguinaria canadensis) with double flowers at Eloise Butler you say? Yes, for a number of years they bloomed in the Garden and toward the last they were only found along the path from the front gate down to the Martha Crone Shelter. They died out soon after the photo below was taken.
It is believed that they came from former curator Martha Crone's home garden in 1988 when her family donated a number of plants to the Garden at the time Martha entered a nursing home. They are a naturally occurring native species but not common. Martha kept a record in her correspondence of May 1968 of sending some of them from her home garden to several friends - a Gladys Mockford in Blackduck, MN and a Mrs. Eldred (Blanch) C. Mather in Green, Iowa (note1). The double has the same leaf and structure as the native variety, but the excess of petals nearly hides the yellow color of the stamens.
They are available in the nursery trade as Sanguinaria canadensis - 'Multiplex'. For details of the common variety - see this info sheet.