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Sparganium

While most species produce rosettes of ribbon-like submersed leaves, or leaves partially floating (near the tips) when subjected to high water levels, only two large species, Sparganium angustifolium and S. fluctuans are consistently deeper water species with long floating leaves, sometimes forming extensive colonies with few or no flowering plants. The tiny S. natans also often has floating leaves, but is very short and typically fruits commonly.  

The  submersed leaves of Sparganium superficially resemble those of Vallisneria but are readily distinguished by their fine checkered venation pattern. Floating leaves are generally not distinctly keeled, while erect leaves are strongly keeled (triangular in cross-section).

Sparganium glomeratum occurs in the western Lake Superior region of Minnesota and Ontario, and Wisconsin, and could be found in Northern Michigan. It is terrestrial and like a small plant of S. emersum, but with the beak of the fruit only ca. 1.3–1.8 mm long and the staminate heads usually only 1 or 2.

 

1. Stigmas 2, separate, at end of beak; mature achenes broadly obpyramidal, truncate (flattish on end except for beak), 5–8 mm across at widest part.

S. eurycarpum

1. Stigma 1, mostly on side of beak; mature achenes tapering about equally toward base and apex, about 1–3 mm across at widest part.

2. Beak about 0.5–1.2 (–1.5) mm long (including stigma); fruiting heads at most 10–12 mm in diameter (including beaks); staminate head (often gone by fruiting time) 1 (rarely 2); anthers 0.3–0.6 mm long.

S. natans

2. Beak about 1.5–7 mm long; fruiting heads 12–30 mm in diameter; staminate heads (before falling) 2 or more; anthers various.

3. Mature fruiting heads about 15–20 mm in diameter, in a branched inflorescence; leaves flaccid, floating, (3–) 5–9 mm broad; sepals short, reaching at most to middle of body of achene, attached near middle or base of stalk; achenes a dark reddish brown, with beaks ca. 2 (–3) mm long and rather strongly curved from their bases; stigmas and anthers ca. 0.3–0.7 mm long.

S. fluctuans

3. Mature heads 20–30 mm in diameter or if smaller the inflorescence unbranched (at most the lowest head peduncled); leaves erect or if floating usually not over 5 mm wide; sepals extending beyond middle of body of achene, usually attached at or near summit of stalk; achenes dark brownish (in S. americanum and S. androcladum) or greenish to yellow-green, the beaks 2.5–7 mm long, usually rather straight or only slightly curved; stigmas and anthers various.

4. Pistillate heads (or branches or stalks) all borne directly in the axils of the leaves or bracts, 20–30 mm in diameter at maturity.

5. Stigmas 0.8–1.5 (–2) mm long; body of mature achene rather dull, dark greenish brown, slightly if at all ribbed at summit, 4–5 mm long, with beak 2.5–4 (–5) mm long; anthers 0.6–1.1 mm long.

S. americanum

5. Stigmas 2–3.2 mm long; body of mature achene darkish but shiny, about 6 mm long, with numerous rather prominent ribs at summit, the beak 5–7 mm long; anthers 1.1–1.4 mm long.

S. androcladum

4. Pistillate heads (at least some heads or stalks) supra-axillary (borne some distance above the axils), rarely all axillary in S. emersum, 12–28 mm in diameter at maturity.

6. Leaves floating (except in a rare semi-terrestrial form); beak of achene ca. 1.5–2.5 mm long, usually shorter than body at maturity; fruiting heads about 15–18 mm in diameter.

S. angustifolium

6. Leaves usually stiffly erect (rarely floating); beak of achene ca. 3–5 mm long, usually equaling body; fruiting heads mostly 20–28 mm in diameter (beaks shorter and heads as small as 12 mm in a form with short stem and crowded heads).

S. emersum

All species found in Sparganium

Sparganium americanumAMERICAN BUR-REED 
Sparganium androcladumBUR-REED 
Sparganium angustifoliumNARROW-LEAVED BUR-REED 
Sparganium emersumGREEN-FRUITED BUR-REED 
Sparganium eurycarpumCOMMON BUR-REED 
Sparganium fluctuansBUR-REED 
Sparganium natansSMALL BUR-REED 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. May 24, 2017. http://michiganflora.net/genus.aspx?id=Sparganium.