From 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]
From WordNet (r) 3.0 (2006) :
Ledum
n 1: evergreen shrubs of north temperate regions [syn: Ledum,
genus Ledum]