Water caltrop, what is it?
The bizarre, ornately shaped fruit or "corm" (the swollen tip of an underground stem) of a water plant that grows in freshwater ponds and streams in Indonesia, southern China, Japan, Italy, and tropical America. The water caltrop is also known as the European water chestnut, buffalo-head fruit, bull nut and Jesuits' nut. Not to be confused with the familiar sweet-and-crunchy Chinese water chestnut, the water caltrop is actually toxic if eaten raw.
Link (here) to the Winnipeg Free Press