The Collaborative International Dictionary of English v.0.48:

man-of-the-earth \man-of-the-earth\ n.
   1. (Bot.) A long-rooted morning glory (Ipomoea leptophylla)
      of Western U. S.

   Syn: man of the earth, Ipomoea leptophylla.
        [WordNet 1.5]

   2. A tropical American prostrate or climbing herbaceous
      perennial (Ipomoea panurata or Ipomoea fastigiata)
      having an enormous starchy root; sometimes held to be
      source of the sweet potato.

   Syn: wild potato vine, wild sweet potato vine, man of the
        earth, manroot, scammonyroot, Ipomoea panurata,
        Ipomoea fastigiata.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Ipomoea panurata
    n 1: tropical American prostrate or climbing herbaceous
         perennial having an enormous starchy root; sometimes held
         to be source of the sweet potato [syn: wild potato vine,
         wild sweet potato vine, man-of-the-earth, manroot,
         scammonyroot, Ipomoea panurata, Ipomoea fastigiata]