Adapted from: Illinois Wildflowers.Info
Photo from: Wikipedia
The flowers of Lilium philadelphicum can be remarkably large, considering its size. This is arguably one of the most beautiful native wildflowers. Other native lilies (Lilium spp.) are usually taller plants with whorled leaves and drooping flowers; only the flowers of Prairie Lily (Lilium philadelphicum) remain erect. One reason why this plant has erect flowers is that the anthers can close their pores temporarily in response to rain, thereby protecting the pollen (Edwards & Jordan, 1992). This is a highly unusual characteristic. The typical variety of this plant is the more eastern Wood Lily (Lilium philadelphicum philadelphicum). The Wood Lily differs from the Prairie Lily in being a slightly taller plant that has mostly whorled leaves, its leaves are usually wider (often exceeding ½" across), and its seed capsules are slightly shorter. In the past, the Prairie Lily was sometimes classified as a distinct species, or Lilium umbellatum. Other common names for this plant are Western Lily and Wood Lily. There are also yellow-flowered forms of this species.