The Collaborative International Dictionary of English v.0.48:

pearly everlasting \pearly everlasting\ n. (Bot.)
   an American everlasting (Anaphalis margaritacea) having
   foliage with soft wooly hairs and corymbose heads with
   pearly-white scarious involucres.

   Syn: cottonweed, Anaphalis margaritacea.
        [WordNet 1.5 +MW10]

WordNet (r) 3.0 (2006):

pearly everlasting
    n 1: an American everlasting having foliage with soft wooly
         hairs and corymbose heads with pearly white bracts [syn:
         pearly everlasting, cottonweed, Anaphalis
         margaritacea]