The Collaborative International Dictionary of English v.0.48:

Immortelle \Im`mor*telle"\, n.; pl. Immortelles. [F. See
   Immortal.] (Bot.)
   A plant with a conspicuous, dry, unwithering involucre, as
   the species of Antennaria, Helichrysum, Gomphrena, etc.
   See Everlasting.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Helichrysum \Hel`i*chry"sum\, n. [L., the marigold, fr. Gr. ? a
   kind of plant.] (Bot.)
   A genus of composite plants, with shining, commonly white or
   yellow, or sometimes reddish, radiated involucres, which are
   often called "everlasting flowers."
   [1913 Webster]

WordNet (r) 3.0 (2006):

Helichrysum
    n 1: large genus of mostly African and Australian herbs and
         shrubs: everlasting flowers; in some classifications
         includes genus Ozothamnus [syn: Helichrysum, genus
         Helichrysum]