Genus Eryngium
- Description, photograph and cultivation tips for three Eryngiums.
- http://www.findmeplants.co.uk/Eryngium-genus.aspx

Eryngium
- Photographs of five species with brief notes.
- http://tomclothier.hort.net/album/eryngium.htm

Eryngium: Sea Holly
- An article on sea hollies from the Colorado State University, covering some of the types available and their cultivation in the United States.
- http://coopext.colostate.edu/4dmg/Flowers/Perenls/seaholly.htm