Silphium perfoliatum
USDA-NRCS PLANTS Database / USDA NRCS. Wetland flora: Field office illustrated guide to plant species. USDA Natural Resources Conservation Service. - Not copyrighted image - Foto visualizzata 473 volte

Silphium perfoliatum
Douglas Ladd - USDA-NRCS PLANTS Database / USDA SCS. 1989. Midwest wetland flora: Field office illustrated guide to plant species. Midwest National Technical Center, Lincoln. - Not copyrighted image - Foto visualizzata 476 volte

Silphium perfoliatum
USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. Vol. 3: 460. - Foto visualizzata 486 volte

Silphium perfoliatum
Dipartimento di Scienze della Vita, Università di Trieste - Progetto Dryades - Picture by Andrea Moro - Parigi, Jardin des plantes., Francia, - Image licensed under a Creative Commons Attribution Non Commercial Share-Alike 3.0 License - Foto visualizzata 532 volte