Silphium L.
Silphium is a North American genus of 12 species (23 according to Brown 2000 but a broader species concept is currently applied; see Clevinger 2004). Three species are cultivated as ornamentals in Europe (Brown 2000; Jäger & al. 2008) but only one, Silphium perfoliatum, is more or less widely cultivated. Silphium trifoliatum L. is now subsumed under S. asteriscus L. (var. trifoliatum (L.) J.A. Clevinger) (see Clevinger 2004, 2006).
Literature
Brown N. (2000) Silphium. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 660-661.
Clevinger J.A. (2006) Silphium. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 21. Oxford University Press, New York-Oxford: 77-82.
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.