Kew Millennium Seed Bank, UK
Seed from the Kew Millennium Seed Bank collection at Wakehurst, outside London in the UK.
Trapa natans (Lythraceae) - water caltrop, water chestnut, horn nut; native to Eurasia & Africa
Trapa natans (water caltrop, horn nut), has been cultivated in China for more than three thousand years but the crunchy water chestnuts commonly used in Chinese cooking are the fleshy corms (not seeds) of the totally unrelated spike rush (Eleocharis dulcis, Cyperaceae).
weblinks:
http://en.wikipedia.org/wiki/Water_caltrop
http://www.invasive.org/species/subject.cfm?sub=3499
