Sparganium androcladum
Sparganium hyperboreum
branch bur-reed, branching bur-reed, rubanier rameux
northern bur-reed, rubanier hyperboréal
stiff, keeled from base at least to middle, flattened distally, to 1.2 m × 5–15 mm.
limp, unkeeled, flat, 0.1–0.4(–0.8) m × 1–5 mm.
rachis (0–)1–3 branched, erect, bracts strongly ascending, not basally inflated; pistillate heads (1–)2–4 on main rachis, 0(–2) on lateral branches, axillary, not contiguous, sessile or short-peduncled, 2.5–3.5 cm diam. in fruit; staminate heads 3–8 on main rachis, 1–6 on lateral rachises, most not contiguous.
rachis unbranched, flexuous;
bracts ascending, lower bracts slightly inflated near base; pistillate heads 1–4, axillary, contiguous, sessile, or most proximal peduncled and supra-axillary, 0.5–1.4 cm diam. in fruit; staminate heads 1(–2), terminal, contiguous or not with distalmost pistillate head.
tepals often with prominent subapical dark spot, subentire to entire;
stigma 1, linear.
tepals without subapical dark spot, erose;
stigmas 1, ovate.
brown, proximally dull, distally shiny, subsessile to short-stipitate, fusiform, usually constricted near equator, body not strongly faceted, 5–7 × 2.5–3 mm, tapering to beak;
beak often curved and hooked, 4–7 mm;
tepals attached at base, reaching to equator or somewhat beyond.
brown or yellowish, dull, subsessile, body ellipsoid to obovoid, not faceted, ±more or less constricted at equator, 2–5 × 1.5–2.5 mm;
beak less than 0.5 mm, or absent;
tepals attached at base, not reaching equator.
1.
1.
= 30.
Sparganium androcladum
Sparganium hyperboreum
Sparganium androcladum is less variable than the similar and more common S. americanum, from which it is distinguished by its generally larger size and more robust habit; leaves stiffer, wider, more strongly keeled; inflorescence branches usually without pistillate heads, the bracts ascending; fruiting heads larger; fruits distally shiny, the beak longer and hooked. Immature fruits of S. androcladum resemble mature fruits of S. americanum. Some specimens will not key readily to either species. The complex nomenclatural history is discussed by C. D. K. Cook and M. S. Nicholls (1987).
Sparganium androcladum has an unusual, discontinuous distribution, which is wholly within the range of S. americanum, except in the central Mississippi Valley (M. L. Fernald 1922b). In the absence of convincing specimens, the presence of S. androcladum in Virginia cannot be confirmed, although E. O. Beal (1960) reported it there, and it occurs nearby in West Virginia.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Sparganium hyperboreum is distinguished from other floating-leaved species by its beakless fruits with sessile stigmas.
Putative hybrids between Sparganium hyperboreum and S. natans have been found in Manitoba, Newfoundland, Northwest Territories, and Alaska by V. L. Harms (1973), who discussed variation in both species. The hybrids have wider (2–5 mm) leaves, golden-brown fruits with short (1 mm) beaks, and supra-axillary pistillate heads (V. L. Harms 1973; C. D. K. Cook and M. S. Nicholls 1986).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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