Eleocharis compressa
Eleocharis aestuum
flat-stem spikerush, flat-stem spikesedge, unknown
tidal spikerush, tidal spikesedge
subterete to greatly compressed, to 5 times as wide as thick, often with 2–12 ridges, 8–45 cm × (0.2–)0.5–1.8 mm, firm to hard, spongy.
often spreading or declining, 3–30 cm × 0.5–1 mm.
distal leaf sheaths persistent, not splitting, proximally red, distally green to stramineous, papery, apex usually red-brown, broadly obtuse to subtruncate, callose, tooth absent.
apex of distal leaf sheath obtuse, tooth to 0.2(–0.5) mm.
ovoid, 4–8 × 2–4 mm, apex acute;
proximal scale clasping 3/4 of culm to amplexicaulous, entire;
subproximal scale empty or with flower;
floral scales spreading in fruit, 20–60, 6 per mm of rachilla, medium brown to very dark brown, sometimes stramineous or colorless, midrib region often paler, ovate, 2–3(–4) × 1–1.5 mm, apex acute to acuminate, the apical colorless hyaline region mostly longer than wide and 0.6–1.2 mm, in proximal part of spikelet 2-fid to shallowly cut, rarely entire, in distal part often entire, carinate in distal part of spikelet.
ellipsoid to ovoid, 3–10 × 2–4 mm, apex blunt to subacute;
floral scales 10–100+, 10 per mm of rachilla, colorless to pale brownish except for green midrib, 1.5–2 × 1 mm, midribs not keeled, apex rounded.
perianth bristles 0–5, stramineous, length variable, to equaling achene, obscurely to clearly retrorsely spinulose;
stamens 3;
anthers yellow- to orange-brown, 0.7–2 mm;
styles 3-fid or some 2-fid.
perianth bristles absent or 2–4, stramineous or whitish, shorter than to nearly 1/2 achene, very slender, without spinules;
stamens 2(–3);
anthers 0.3–0.5 mm;
styles 2-fid or some 3-fid.
falling with scales or some persistent, yellow-brown or dark brown, obovoid to obpyriform, nearly equilaterally to compressed-trigonous or usually some biconvex, angles evident or obscure, 0.8–1.1 × 0.6–0.8 mm, neck very short, finely rugulose and sometimes finely (or coarsely) cancellate at 10–20X with 14–20 blunt horizontal ridges in a vertical series.
0.75–1 × 0.6–0.8 mm.
brown (to whitish), pyramidal, usually depressed, often rudimentary, 0.15–0.3 × 0.2–0.35 mm.
deltoid, 0.2–0.3 × 0.35–0.45(–0.55) mm, 1/2–3/4as high as wide, 1/4–1/3 as high and 1/2–2/3(–4/5) as wide as achene.
Eleocharis compressa
Eleocharis aestuum
Varieties 2 (2 in the flora).
Eleocharis compressa is extremely variable. After E. bifida and E. occulta are segregated from E. compressa (type from Ohio) and E. acutisquamata (type from Texas), the remaining plants intergrade completely and are best treated as varieties of E. compressa (S. G. Smith 2001). Because some plants of E. compressa approach E. elliptica some authors have treated E. compressa as a synonym of E. elliptica. Putative E. compressa × E. erythropoda hybrids from southeastern Ontario have been described (P. M. Catling 1994), and I have observed similar putative hybrids in the field in southeastern Wisconsin. Introgression from E. erythropoda is suggested by the presence in many plants of E. compressa of some 2-fid styles and biconvex achenes and some or rarely all entire floral scales, including the type. Some collections of E. compressa from the District of Columbia region and Tennessee have distinctly cancellate achenes as is common in E. tenuis var. verrucosa. The earlier name E. acuminata (Muhlenberg) Nees, name confused (H. K. Svenson 1932), is often given as a synonym of E. compressa (S. G. Smith 2001).
Both 2n = 24 and 2n = 26 cytotypes for E. compressa from south-central United States have been reported (L. J. Harms 1972). Fertile artificial hybrids between these two cytotypes were also reported, as well as artificial E. compressa (2n = 36) × E. elliptica (2n = 38) hybrids with meiotic pairing and pollen stainability more than 90 percent. I have not seen voucher specimens for those artificial hybrids or for any of the published chromosone number reports for E. compressa, except for a count of 2n = 24 (presumably made by L. J. Harms) that is given on a herbarium specimen label of E. compressa var. acutisquamata from Kansas (S. G. Smith 2001).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Eleocharis aestuum is very similar to E. diandra and E. ovata; E. diandra differs from E. aestuum in its lower tubercles, brown floral scales, and absence of perianth bristles; E. ovata differs as given in the key to species. D. M. Hines (1975) described E. aestuum using the epithet “palidostachys” [ined.]. Specimens from shores of the Lake-of-the-Woods in Minnesota, and a reservoir and farm in Hardin and Fayette counties, Tennessee, may be referable to E. aestuum. The only recent records of E. aestuum are from the Androscoggin and Kennebec rivers in Maine and the Hudson River in New York (A. Haines 2001).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Culms compressed, 2–5 times as wide as thick, 0.5–1.8 mm wide. | var. compressa |
1. Culms subterete to slightly compressed, not more than 2 times as wide as thick, (0.2–)0.5–1 mm wide. | var. acutisquamata |
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