The Collaborative International Dictionary of English v.0.48:

Ledum \Ledum\ prop. n.
   A genus of evergreen shrubs of the north temperate regions.

   Syn: genus Ledum.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Ledum
    n 1: evergreen shrubs of north temperate regions [syn: Ledum,
         genus Ledum]