The Collaborative International Dictionary of English v.0.48:

mandrake \man"drake\ (m[a^]n"dr[=a]k), n. [AS. mandragora, L.
   mandragoras, fr. Gr. mandrago`ras: cf. F. mandragore.]
   1. (Bot.) A low plant (Mandragora officinarum) of the
      Nightshade family, having a fleshy root, often forked, and
      supposed to resemble a man. It was therefore supposed to
      have animal life, and to cry out when pulled up. All parts
      of the plant are strongly narcotic. It is found in the
      Mediterranean region.
      [1913 Webster]

            And shrieks like mandrakes, torn out of the earth,
            That living mortals, hearing them, run mad. --Shak.
      [1913 Webster]

   Note: The mandrake of Scripture was perhaps the same plant,
         but proof is wanting.
         [1913 Webster]

   2. (Bot.) The May apple (Podophyllum peltatum). See May
      apple under May, and Podophyllum. [U.S.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

Mandragora officinarum
    n 1: a plant of southern Europe and North Africa having purple
         flowers, yellow fruits and a forked root formerly thought
         to have magical powers [syn: mandrake, devil's apples,
         Mandragora officinarum]