Ageratum L.
Ageratum is a New World genus of ca. 40 species, most native to Central and South America. Some species are cultivated as ornamentals (see Galloway & Richardson 2000, Jäger & al. 2008) but only one is widespread in cultivation (Ageratum houstonianum). A few have become more or less pantropical weeds.
Literature:
Galloway A.A. & Richardson J.E. (2000) Ageratum. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 661-662.
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
Johnson M.F. (1971) A monograph of the genus Ageratum L. (Compositae-Eupatorieae). Ann. Missouri Bot. Gard. 58: 6-88.
Nesom G.L. (2006) Ageratum. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 21. Oxford University Press, New York-Oxford: 481-483.
Robinson H. (1990) Notes on Ageratum in Mesoamerica (Eupatorieae : Asteraceae). Phytologia 69(2):
93-104.