Source : Webster's Revised Unabridged Dictionary (1913)

Frostweed \Frost"weed`\, n. (Bot.)
   An American species of rockrose ({Helianthemum Canadense}),
   sometimes used in medicine as an astringent or aromatic
   tonic.

   Note: It has large yellow flowers which are often sterile,
         and later it has abundant but inconspicuous flowers
         which bear seed. It is so called because, late in
         autumn, crystals of ice shoot from the cracked bark at
         the root; -- called also frostwort.

Source : WordNet®

Helianthemum canadense
     n : perennial of the eastern United States having early solitary
         yellow flowers followed by late petalless flowers;
         so-called because ice crystals form on it during first
         frosts [syn: {frostweed}, {frost-weed}, {frostwort}, {Crocanthemum
         canadensei}]