The Collaborative International Dictionary of English v.0.48:

Birthroot \Birth"root`\, n. (Bot.)
   An herbaceous plant (Trillium erectum), and its astringent
   rootstock, which is said to have medicinal properties.
   [1913 Webster]

WordNet (r) 3.0 (2006):

birthroot
    n 1: trillium of eastern North America having malodorous pink to
         purple flowers and an astringent root used in folk medicine
         especially to ease childbirth [syn: purple trillium, red
         trillium, birthroot, Trillium erectum]