Trichophorum cespitosum
Tufted Bulrush

Achene, Two Views

Greenbush Bog, 20 km West of Hudson Bay, SK on Highway #3

Note the achene is trigonous.

I had originally identified this species as Eleocharis quinquefolia.  The correct identification was provided by Anna Leighton and I very much appreciate her doing this.  Anna is currently working on the next fascicle that will be published by the Flora of Saskatchewan Association.  That publication (Rushes, Bulrushes and Pondweeds, plus the remaining Monocots of Saskatchewan by Vern Harms, Anna Leighton and Mary Vetter) will cover both Eleocharis and Trichophorum.