Source : Webster's Revised Unabridged Dictionary (1913)

Peppergrass \Pep"per*grass`\, n. (Bot.)
   (a) Any herb of the cruciferous genus {Lepidium}, especially
       the garden peppergrass, or garden cress, {Lepidium
       sativum}; -- called also {pepperwort}. All the species
       have a pungent flavor.
   (b) The common pillwort of Europe ({Pilularia globulifera}).
       See {Pillwort}.

Source : WordNet®

Pilularia globulifera
     n : European water fern found around margins of bodies of water
         or in wet acid soil having small globose sporocarps [syn:
          {pillwort}]