The Collaborative International Dictionary of English v.0.48:

Juncus \Juncus\ n.
   The type genus of the Juncaceae, comprising the rushes;
   they are perennial tufted glabrous marsh plants of temperate
   regions.

   Syn: genus Juncus.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Juncus
    n 1: type genus of the Juncaceae; perennial tufted glabrous
         marsh plants of temperate regions: rushes [syn: Juncus,
         genus Juncus]