Conyza sumatrensis is recognized as distinct from C. bonariensis and C. canadensis. Conyza albida and C. floribunda are treated as synonyms of C. sumatrensis. Conyza sumatrensis includes two varieties, and the new combination C. sumatrensis var. leiotheca is made for the nontypical variety, which is restricted to the Americas. Conyza sumatrensis var. sumatrensis is newly reported and documented in the United States; it also is found widely elsewhere in the Americas and is the sole variety occurring in the Old World.
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Pruski et al. (2006) studied this question.
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