Equisetum x schaffneri 
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http://www.botany.hawaii.edu/faculty/carr/images/equ_sp.jpgEquisetum x schaffneri 
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http://www.botany.hawaii.edu/faculty/carr/images/equ_xsc_cu.jpg
World of Equisetum 
Detailed species accounts of the horsetails (Equisetum subgenus Equisetum).
http://members.eunet.at/m.matus/
Equisetum giganteum Expedition 
Personal account of a trip to find Giant Horsetails in Costa Rica.
http://planeta.clix.pt/welwitschia/equisetum/
Giant Horsetails 
Detailed information about Equisetum giganteum, E. myriochaetum, and E. x schaffneri. Includes photos of wild plants and links.
http://www.fiu.edu/~chusb001/giant_equisetum.html
Horsetails: Relic Plants from Prehistory 
Photographic study by Dave Walker of these plants, including photomicrographs of the cross section of a cone.
http://www.microscopy-uk.org.uk/mag/artjun99/dwhtail.html