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]