The Collaborative International Dictionary of English v.0.48:

Gladen \Gla"den\, n. [AS. gl[ae]dene, cf. L. gladius a sword.
   Cf. Gladiole.] (Bot.)
   Sword grass; any plant with sword-shaped leaves, especially
   the European Iris f[oe]tidissima. [Written also gladwyn,
   gladdon, and glader.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

gladdon \glad"don\ n.
   An iris (Iris foetidissima) with purple flowers and
   evil-smelling leaves; Southern and Western Europe and North
   Africa.

   Syn: gladen, stinking iris, gladdon iris, stinking gladwyn,
        roast beef plant, Iris foetidissima.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

gladdon
    n 1: iris with purple flowers and foul-smelling leaves; southern
         and western Europe and North Africa [syn: stinking iris,
         gladdon, gladdon iris, stinking gladwyn, roast beef
         plant, Iris foetidissima]