Triglochin palustre
 
Marsh Arrow-Grass

Flower, Stage 4

Hudson Bay, SK
26-July-2017

There are three outer tepals and three inner tepals.  Each tepal subtends an anther.  The outer tepals open up and expose their anther (and then largely fall off) before the inner tepals do.  There are three stigmas, although the individual stigmas are difficult to distinguish in this photo.