From 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]
From WordNet (r) 3.0 (2006) :
Antennaria
n 1: small woolly perennial herbs having small whitish discoid
flowers surrounded by a ring of club-shaped bristles [syn:
Antennaria, genus Antennaria]