Sparganium androcladum
Sparganium natans
branch bur-reed, branching bur-reed, rubanier rameux
arctic bur-reed, rubanier nageant, small bur-reed, small bur-reedl
stiff, keeled from base at least to middle, flattened distally, to 1.2 m × 5–15 mm.
limp in water, unkeeled, flat, 0.04–0.6 m × 2–6(–10) mm;
leaves of stranded plants shorter, firmer.
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, basally inflated; pistillate heads 1–3, axillary, not contiguous, sessile or most proximal short-peduncled (often long-peduncled in Alaska and nw Canada), 0.5–1.2 cm diam. in fruit; staminate head 1 or apparently so, terminal, not contiguous 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, lance-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.
dark greenish or brownish, subsessile, body ellipsoid to obovoid, not faceted, barely or not constricted at equator, 2–4 × 1–1.5 mm, tapering to beak;
beak curved, 0.5–1.5 mm;
tepals attached at base, reaching about to equator.
1.
1.
= 30.
Sparganium androcladum
Sparganium natans
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.)
This species has long been known as Sparganium minimum, but although the correct name is S. natans (C. D. K. Cook 1985).
The leaves of Sparganium natans are thinner and more translucent than those of the similar S. hyperboreum, and they lack the yellowish cast of that species. Its distalmost pistillate head is not contiguous with the staminate head, as is sometimes the case in S. hyperboreum, and its beaked fruit also distinguishes it from that species. See the discussion under S. hyperboreum for a description of S. hyperboreum × S. natans.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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