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]