Bolboschoenus fluviatilis
 
River Bulrush

Flower

Hudson Bay Regional Park
04-July-2013

Note the six retrorsely barbellate bristles, the three stamens (one of the anthers has fallen off), and the three-branched style.

This species is now called Bolboschoenus fluviatilis.  However, both Budd's Flora and Flora of Alberta call it Scirpus fluviatilis and this is what is used in the answers to the keys listed below.

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Fluviatilis: Answers to key questions in Budd's Flora and Flora of Alberta leading to this species. 
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rhizomes with swollen nodes; NOT [rhizomes lacking swollen nodes]

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culms mostly 10-15 dm high; NOT [culms mostly 3-7 dm high]

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cauline leaves usually well developed; NOT [cauline leaves usually much reduced]

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involucre green, with the bract or bracts erect or leaf-like, spreading; NOT [involucre consisting of 1 scale-like bract]

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involucre of several leaf-like bracts, spreading; NOT [involucre a single erect bract, appearing as a continuation of the stem], NOT [involucral bract absent]

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inflorescence appearing terminal; NOT [inflorescence appearing lateral]

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spikelets in head-like or umbellate clusters; NOT [spikelets in compound umbels or dense umbellate heads], NOT [spikelets in a much branched inflorescence]

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spikelets in part sessile or subsessile, in part 1-4 at the tip of peduncles to 10 cm long; NOT [spikelets all sessile or subsessile, or in part sessile, in part on peduncles to 5 cm long]

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spikelets 2-12; NOT [spikelets numerous]

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spikelets 10-50 mm long; NOT [spikelets 3-10 mm long]

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style 3-branched; NOT [style 2-branched]

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achene 3-angled; NOT [achene lens-shaped]

 

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Scirpus: Answers to key questions in Budd's Flora and Flora of Alberta leading to this genus. 
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flowers perfect, with spikelets uniform; NOT [flowers imperfect, with staminate and pistillate flowers in same or different spikelets]

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scales of the spikelets several ranked, spirally imbricate; NOT [scales of the spikelets 2-ranked]

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spikelets solitary and terminal or partly lateral; NOT [spikelets in simple or compound terminal umbels] (BF)

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NOT [spikelets in terminal heads or spikes] (FOA)

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scales of the spikelets NOT keeled

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perianth usually present as bristles; NOT [perianth lacking]

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perianth bristles 1-6, rarely lacking; NOT [bristles numerous]

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perianth bristles usually a little longer or shorter than the achene, elongating only in S. hudsonianus; NOT [perianth bristles often 2-3 cm long, silky]

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achenes not enclosed in a perigynium or bract

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base of style not persistent, the achene without a tubercle; NOT [base of the style persistent as a tubercle on top of the achene]

 

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

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