Water caltrop : The water chestnut.

Example:


Taxonomy
water caltrop, water chestnut, seeds, Trapa natans, fruits, free encyclopedia, plant, Trapa bicornis, aquatic plants, The Chinese, species, stem, food, types of leaves, rosette, nut, southern Germany, the seeds.

Defination from the web:
water caltrop was an important food for worship as prayer offerings. ... The Chinese Herbal Medicine Summary (本草備要 published in 1694, written by Wang Ang 汪昂) indicates that water caltrop can help fever and drunkenness. ...