Eleocharis compressa
Eleocharis nigrescens
flat-stem spikerush, flat-stem spikesedge, unknown
black spikerush
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.
sometimes ascending, subterete, elliptic, or polygonal, (1–)3–7.5(–9) cm × 0.2–0.5 mm, very soft.
distal leaf sheaths persistent, not splitting, proximally red, distally green to stramineous, papery, apex usually red-brown, broadly obtuse to subtruncate, callose, tooth absent.
distal leaf sheaths persistent or disintegrating, colorless, stramineous or green, spotted red-brown to purple, membranous, apex narrowly acute.
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.
basal spikelets absent; never proliferous, ovoid or ellipsoid, terete, 2–4.7(–8.5) × 1–2 mm, apex acute to blunt;
proximal scale empty or with flower, persistent, clasping 1/2 of culm, similar to floral scales (but 1.1–1.7 mm, midrib region broadly green);
subproximal scale with a flower;
floral scales spiraled, 10–30(–100), 10–16 per mm of rachilla, colorless, whitish, or pale brown, mottled red-brown to purple, midribs pale brown or green, ovate or elliptic, 1–1.2 × 0.45–0.6 mm, membranous, midrib prominent, 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 absent;
stamens 1;
anthers 0.2–0.3 mm;
styles 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.
colorless (appearing green-brown from enclosed seed) or whitish, sometimes spotted red-brown, obovoid, trigonous, angles prominent, 0.5–0.6 × 0.33–0.4 mm, apex constricted proximal to tubercle, smooth.
brown (to whitish), pyramidal, usually depressed, often rudimentary, 0.15–0.3 × 0.2–0.35 mm.
white, gray or pale brown, pyramidal or umbonate, trigonous, 0.1–0.15 × 0.15–0.2 mm.
Eleocharis compressa
Eleocharis nigrescens
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.)
Usually all the floral scales fall from the rachilla at maturity. The achene epidermis is usually translucent, revealing the brown color of the enclosed seed.
Clarification of delimitation of Eleocharis microlepis (Grisebach) D. A. Simpson, E. setifolia, (A. Richard) A. Raynal, and E. nigrescens in the Americas requires further investigation (D. A. Simpson 1988). Specimens from North America treated herein as E. nigrescens seem to agree well with Simpson’s illustration of E. nigrescens; the anther length of 0.2–0.3 mm recorded here is closer to that of E. microlepis. Simpson (pers. comm.) has not examined specimens of either E. nigrescens or E. microlepis from North America, and lists both E. microlepis and E. setifolia from the West Indies and only E. setifolia from South America.
(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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