Sparganium androcladum
Sparganium americanum
branch bur-reed, branching bur-reed, rubanier rameux
American bur-reed, rubanier d'amérique
stiff, keeled from base at least to middle, flattened distally, to 1.2 m × 5–15 mm.
erect but not especially stiff, usually keeled only near base, flattened distally, to 1 m × 6–12 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 0–3-branched, erect;
bracts somewhat ascending, not basally inflated; pistillate heads 1–3 on branches, 2–6 on main rachis, axillary, not contiguous at anthesis, sessile, 1.5–2.5 cm diam. and often contiguous in fruit; staminate heads usually 3–7 on each branch, 4–10 on main rachis, not or barely contiguous.
tepals often with prominent subapical dark spot, subentire to entire;
stigma 1, linear.
tepals often with prominent subapical dark spot, entire to crenulate or emarginate;
stigma 1, linear-lanceolate.
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.
tan to dark greenish brown, dull, subsessile to stipitate, fusiform, sometimes barely constricted near equator, body not strongly faceted, 3.5–5(–7) mm, tapering to beak;
beak usually curved, not hooked, 3–5 mm;
tepals attached at base, reaching equator or slightly beyond.
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Sparganium androcladum
Sparganium americanum
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.)
For differences between this highly polymorphic species and the similar but less variable Sparganium androcladum, see the discussion under that species. Also see the discussion under S. emersum.
E. O. Beal (1977) recognized three morphologically overlapping races of Sparganium americanum: the coastal race, growing in the lower coastal plain from Virginia to Florida and Louisiana, and north in the Mississippi Embayment to Oklahoma, Arkansas, and Missouri, has leaves wide for the species, rachises 2–5-branched, and stigmas 1.5+ mm long; the Appalachian race, growing in the Appalachian region from Maine to western North Carolina and in the Ozark Mountains, has leaves narrow for the species, rachises simple to sparingly branched, and stigmas 0.9 mm or less; and the ubiquitous race, growing throughout the range of the species with increasing robustness southward, morphologically overlaps the others.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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