The Collaborative International Dictionary of English v.0.48:

club moss \club" moss`\, clubmoss \clubmoss\n. (Bot.)
   a primitive evergreen mosslike plant with spores in
   club-shaped strobiles, much used in winter decoration. The
   best known species is Lycopodium clavatum, but other
   Lycopodia are often called by this name. The spores form a
   highly inflammable powder.

   Syn: club moss, lycopod.
        [1913 Webster + WordNet 1.5]