Eriophorum vaginatum
 
Sheathed Cottongrass

Mature Achene and Bristles

Greenbush Bog, 20 km West of Hudson Bay, SK on Highway #3
12-August-2017

I had originally identified this species as Eriophorum brachyantherum.  The correct identification was provided by Anna Leighton and I very much appreciate her doing this.  The book Rushes, Bulrushes and Pondweeds, plus the remaining Monocots of Saskatchewan, authored by Vern Harms, Anna Leighton and Mary Vetter and published by the Flora of Saskatchewan Association is now available.

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Vaginatum: 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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Spikelets solitary, erect at tip of culm; leaf-like inflorescence bracts absent; distal-most cauline leaves usually reduced to bladeless sheaths; lower scales of spikelets usually empty (without flowers).  NOT [Spikelets usually 2 or more, drooping or spreading on peduncles; leaf-like inflorescence bracts present; distal-most cauline leaves with blades at least 1 cm long and usually longer than their sheaths (shorter in E. gracile); lower scales of spikelets usually fertile (subtending flowers).]

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Plants forming tufts or tussocks; empty lower spikelet scales 7 or more.  NOT [Plants forming colonies from creeping rhizomes, not cespitose; empty lower spikelet scales 7 or fewer.]

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Plants forming tussocks; lower empty scales spreading or reflexed on spikelets in fruit stage and with pale margins to 1 mm wide; bristles usually white, seldom reddish or brown; bladeless cauline sheaths conspicuously expanded at tip.  NOT [Plants forming tufts; lower empty scales ascending on spikelets in fruit stage and scarcely paler at the margins; bristles creamy white to pale brownish; bladeless cauline sheaths not conspicuously expanded at tip.]

 

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Eriophorum: 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 genus. The answers are in the order you would normally work through the key. 
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Flowers and achenes naked in the axils of scales, not enclosed in a sac; flowers usually perfect (sometimes some flowers imperfect in Cyperus, Rhynchospora and Cladium).   NOT [. Flowers and achenes enclosed in a sac (perigynium) borne in the axils of scales; flowers imperfect.]

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Perianth bristles usually more than 10 per flower, much longer than the achenes, conspicuously elongated to over 10 mm long in fruit stage and usually obscuring most scales in spikelets.  NOT [Perianth bristles absent or up to 6 per flower; if more than 6, then only somewhat longer than the achenes.]

 

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Cyperaceae: Answers to key questions in Budd's Flora leading to this family. 
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plants not aquatic, or if growing in water, most of the plant emersed; NOT [plants aquatic, floating or submerged, with floating leaves or emersed inflorescence]

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culms usually solid; NOT culms usually hollow]

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leaves three-ranked; NOT [leaves two-ranked]

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inflorescence NOT [a dense, single, cylindrical spike 8-15 cm long, 1-2.5 cm thick],  if a single spike, less than 1 cm thick

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flowers not in globular heads; NOT [flowers in globular heads, the upper ones staminate, the lower ones pistillate]

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flowers solitary in the axil of a single bract (scale); NOT [flowers enclosed in two-ranked bracts with the lowest (glumes) empty]

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perianth absent or inconspicuous, not in two whorls; NOT [perianth present, conspicuous, in two whorls of 3 segments each, often brightly colored]

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perianth reduced to bristles or scales or lacking; NOT [perianth reduced to minute lodicules or lacking]