Sparganium glomeratum
Sparganium fluctuans
cluster bur-reed, northern bur-reed, rubanier aggloméré
floating bur-reed, rubanier flottant, water bur-reed
stiff, weakly keeled, to 50 cm × 6 mm.
limp, unkeeled, flat, mostly 0.6–1 m × 4–10 mm.
rachis unbranched, condensed, erect;
bracts ascending, somewhat inflated near base; pistillate heads 2–6, mostly supra-axillary, sometimes opposite bract above, upper crowded, sessile, proximal head not contiguous with upperdistal, peduncled, 1.2–1.6(–2) cm diam. and contiguous in fruit; staminate heads 1(–2), contiguous or not with distalmost pistillate head.
rachis 0–2-branched, distal part erect at water surface;
bracts ascending, not inflated at base; pistillate heads 0–2 on main rachis, 1–2 on secondary rachises, axillary or supra-axillary, often some contiguous or nearly so, especially in fruit, sessile, 1.5–2.3 cm diam. in fruit; staminate heads 3–6 on main rachis, 1–4 on secondary rachises, contiguous or not, but not contiguous with distalmost pistillate head.
tepals without subapical dark spot, entire to erose;
stigma 1, lanceolate.
tepals often with prominent apical dark spot, apically erose to fimbriate;
stigmas 1, linear-lanceolate.
greenish brown, lustrous, stipitate, fusiform, body not faceted, slightly constricted near equator, 3–6 × 2–3 mm, tapering to beak;
beak straight, 1.5–2 mm;
tepals attached at base, reaching 1/3 to 1/2 length of fruit.
eventually dark reddish brown, dull, stipitate, elliptic to obovoid or fusiform, body not faceted, sometimes constricted near equator, 2–5 × 1.5–2 mm, tapering to beak;
beak curved, 2–3.5 mm;
tepals borne at middle of fruit stipe, basally adnate to stipe, reaching about nearly to equator.
1.
1.
= 30.
Sparganium glomeratum
Sparganium fluctuans
Sparganium glomeratum is apparently rare, or perhaps is only rarely collected, in North America, except it is locally common in sedge-marshes and black-ash swamps near the western end of Lake Superior. The species is rather invariable throughout its circumboreal range (C. D. K. Cook and M. S. Nicholls 1986).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
The tepals are usually adnate to the fruit stipe for about half their length, but in our other species they are free from it.
Sparganium fluctuans is not known to hybridize. When vegetative, it is sometimes confused with S. angustifolium, but the floating leaves of that species are usually less than 5 mm wide and plano-convex. Sparganium fluctuans is more robust than the grasslike S. natans, with which it sometimes grows.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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