Plants slender to robust, to 0.4(–0.6) m; at least some leaves and inflorescences emergent, erect. Leaves stiff, weakly keeled, to 50 cm × 6 mm. Inflorescences: 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. Flowers: tepals without subapical dark spot, entire to erose; stigma 1, lanceolate. Fruits 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. Seeds 1. 2n = 30.
Phenology: Flowering summer (Jul–Aug).
Habitat: shallow, quiet, neutral, mesotrophic waters
Elevation: 0–1000 m
Alta., B.C., Nfld. and Labr. (Labr.), Ont., Que., Sask., Minn., Wis., circumboreal.
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).