The Collaborative International Dictionary of English v.0.48:

Ragwort \Rag"wort`\ (r[a^]g"w[^u]rt`), n. (Bot.)
   A name given to several species of the composite genus
   Senecio.
   [1913 Webster]

   Note: Senecio aureus is the golden ragwort of the United
         States; Senecio elegans is the purple ragwort of
         South Africa.
         [1913 Webster]

WordNet (r) 3.0 (2006):

Senecio aureus
    n 1: weedy herb of the eastern United States to Texas having
         golden-yellow flowers; sometimes becomes invasive;
         sometimes placed in genus Senecio [syn: golden groundsel,
         golden ragwort, Packera aurea, Senecio aureus]