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 leptophylla
    n 1: a morning glory with long roots of western United States
         [syn: man-of-the-earth, Ipomoea leptophylla]