The Collaborative International Dictionary of English v.0.48:

Starwort \Star"wort`\ (st[aum]r"w[^u]rt`), n. (Bot.)
   (a) Any plant of the genus Aster. See Aster.
   (b) A small plant of the genus Stellaria, having
       star-shaped flowers; star flower; chickweed. --Gray.
       [1913 Webster]

   Water starwort, an aquatic plant (Callitriche verna)
      having some resemblance to chickweed.

   Yellow starwort, a plant of the genus Inula; elecampane.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Water starwort \Wa"ter star"wort`\
   See under Starwort.
   [1913 Webster]

WordNet (r) 3.0 (2006):

water starwort
    n 1: any of several aquatic plants having a star-shaped rosette
         of floating leaves; America, Europe and Asia