- ragwort, tansy ragwort, ragweed, benweed, Senecio jacobaea - widespread European weed having yellow daisylike flowers; sometimes an obnoxious weed and toxic to cattle if consumed in quantity
--1 is a kind of weed
--1 is a member of Senecio, genus Senecio - ragweed, ambrosia, bitterweed - any of numerous chiefly North American weedy plants constituting the genus Ambrosia that produce highly allergenic pollen responsible for much hay fever and asthma
--2 is a kind of weed
--2 is a member of genus Ambrosia
--2 has particulars:common ragweed, Ambrosia artemisiifolia; great ragweed, Ambrosia trifida; western ragweed, perennial ragweed, Ambrosia psilostachya