Horsetails

I think they are the only land plant that has silica as a structural component. As I recall, American pioneers used their stalks to scrub pots and pans due to the abrasive quality, hence their nickname "scouring rushes". I saw them in great profusion in wet forests on Olympia, Washington in 1994 when Jeff and I camped there.  John

http://www.terradaily.com/reports/Hot_Spring_Horsetails_Oldest_Existing_Land_Plant_999.html