Sparganium eurycarpum
 
Giant Bur-Reed

Drupe on Receptacle

Saginas Lake Dam, South of Hudson Bay on Highway # 982
30-July-2019

Note the drupe is sessile, obpyramidal and abruptly contracts to the beak.  Note also that some authors refer to the fruit as an achene, although that is technically incorrect.

See here for a key to Saskatchewan Sparganium species created by Anna Leighton and found in Rushes, Bulrushes & Pondweeds plus the remaining Monocots of Saskatchewan by V.L. Harms,  A.L. Leighton and  M.A. Vetter)

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Eurycarpum: Answers to key questions in Rushes, Bulrushes & Pondweeds plus the remaining Monocots  of Saskatchewan by V.L. Harms, A.L. Leighton and M.A. Vetter leading to this species. The answers are in the order you would normally work through the key.
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Stigmas usually 2, occasionally 1 on some flowers; mature fruit bodies 5-10 mm long, obpyramidal, abruptly contracted to beaks, sessile, usually 2-locular and 2-seeded; inflorescences usually branched; leaves emergent; NOT [Stigmas 1; mature fruit bodies usually <5 mm long, ellipsoidal, fusiform or obovoid, tapering to beaks (+/- beakless in S. hyperboreum), stipitate or subsessile, 1-locular and 1-seeded; inflorescences branched or unbranched; leaves emergent or floating]