The Collaborative International Dictionary of English v.0.48:

Nardoo \Nar*doo"\ (n[aum]r*d[=oo]"), n. (Bot.)
   An Australian name for Marsilea Drummondii, a four-leaved
   cryptogamous plant, sometimes used for food.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Marsilea drummondii
    n 1: Australian clover fern [syn: nardoo, nardo, common
         nardoo, Marsilea drummondii]