S. tabernaemontani  & acutus
     
Great Bulrush & Viscid Great Bulrush

Upper Quarter of Culm, Cross Section Comparison

Regina & White Butte Recreation Area
20-July-2016

Differences between S. acutus and S. tabernaemontani as described in the key 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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Acutus: Culms usually dark green, firm, not easily compressed when fresh; scales narrowly ovate to ovate, longer than achenes (covering them at maturity), usually pale stramineous, but +/- prominently striate or marked with dark reddish brown, with margins often appearing more laciniate-fimbriate than ciliate and awns up to 2 mm long (but often broken off); inflorescences at most 2-times branched, with branches to 6 (18) cm long and usually stiffly ascending. 

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Tabernaemontani: Culms usually pale green, soft, easily compressed when fresh; scales ovate, shorter than or equal to achenes (exposing them at maturity), often uniformly dark reddish brown to paler orange-brown or stramineous, with margins ciliate and awns up to 0.8 mm long; inflorescences 2 - 4-times branched, with branches to 15 (25) cm long and often spreading and drooping.

Schoenoplectus acutis belongs to the very difficult Schoenoplectus lacustris complex.  In fact, one author (T. Koyama) placed all members of the complex in a single species (Scirpus lacustris).  One other member of the complex (Schoenoplectus tabernaemontani) is found in Saskatchewan and the two species occasionally hybridize.  

Different flora have used different characteristics to differentiate between Schoenoplectus acutus and Schoenoplectus tabernaemontani.  The following table lists all of these.  Note that Budd's Flora directly contradicts Flora of the Great Plains regarding the relative lengths of the scale and achene.

Flora S. acutus S. tabernaemontani
Budd's Flora scales much longer than the achenes scales almost as long as the achenes
Budd's Flora scales narrowly ovate scales broadly ovate
Budd's Flora culms firm culms spongy
Budd's Flora spikelets 1-2 cm long spikelets 3-7 mm long
Flora of Alberta culms firm culms soft
Flora of Alberta inflorescence erect, often compact inflorescence often drooping
Flora of Alberta scales laciniate-fimbriate scales ciliolate
Flora of Alberta scales pale with conspicuous reddish brown striae scales a rich chestnut brown
Flora of Alberta achenes 1.8-3.0 mm long achenes 1.4-2.2 mm long
Flora of the Great Plains spikelets usually in glomerules of 3-8 spikelets usually in glomerules of 2, seldom 3 or single
Flora of the Great Plains spikelets sessile or on short stiff pedicels spikelets on long, lax pedicels
Flora of the Great Plains scales shorter than or equal to achenes scales exceeding the achenes
Flora of the Great Plains culms firm culms soft
Flora of the Great Plains culms dark green culms light green
Flora of North America spikelet scale awns (sometimes broken off) mostly strongly contorted, rarely all straight spikelet scale awns straight to bent
Flora of North America spikelet scale awns 0.52 mm spikelet scale awns  0.20.8 mm
Flora of North America scales wholly or partly pale and prominently spotted at 10X scales (except often midribs) uniformly orangish, or sometimes straw-colored and prominently spotted at 10X
Flora of North America scale flanks sparsely to often densely scabrous scale flanks smooth or very sparsely (rarely densely) scabrous
Flora of North America  some spikelets always clustered. spikelets often all solitary
Flora of North America  widest air spaces in upper 1/4 of culm 0.5 (east)1.5(2.5) (west) mm wide. widest air spaces in upper 1/4 of culm 12.5 mm wide.