The Collaborative International Dictionary of English v.0.48:

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.
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pepperwort \Pep"per*wort`\, n. (Bot.)
   See Peppergrass.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pepperwort
    n 1: any of several water ferns of the genus Marsilea having
         four leaflets [syn: clover fern, pepperwort]
    2: annual herb used as salad green and garnish [syn: common
       garden cress, garden pepper cress, pepper grass,
       pepperwort, Lepidium sativum]