This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Characters of the family. [Latin, calcitrapa, the caltrop.] Type species: Trapa natans L.
Trapa natans L. Sp. Pl. 120. 1753.
Rooting in the mud at the bottom of lakes or slow streams; stem often several feet long. Submerged leaves approximate, pectinately dissected, 1'-4' long; floating leaves in a rosette sometimes 1° broad, their blades rhombic-ovate, sharply dentate above, broadly cuneate and entire below, about 1' wide, glabrous and shining above, the conspicuous veins of the lower surface beset with short stiff hairs; petioles of the floating leaves 2'-6' long, inflated and spongy; flowers white, about 3" broad; fruit 1'-2' long, armed with 4 somewhat recurved spines.
Naturalized in ponds and streams, eastern Massachusetts, and near Schenectady, N. Y. Native of Europe. Called also sanghara-nut, Jesuit's water-nut. Seed mealy, edible. June-July.