The Collaborative International Dictionary of English v.0.48:

Birthwort \Birth"wort`\, n.
   A genus of herbs and shrubs (Aristolochia), reputed to have
   medicinal properties.
   [1913 Webster]

WordNet (r) 3.0 (2006):

birthwort
    n 1: creeping plant having curving flowers thought to resemble
         fetuses; native to Europe; naturalized Great Britain and
         eastern North America [syn: birthwort, Aristolochia
         clematitis]