Eleocharis vivipara
Eleocharis nigrescens
sprouting spike-rush, umbrella hairgrass, viviparous spike-rush
black spikerush
often arching, often sering as stolons, broadly elliptic, (4–)7–38(–45) cm × (0.1–)0.3–0.7 mm, soft to firm.
sometimes ascending, subterete, elliptic, or polygonal, (1–)3–7.5(–9) cm × 0.2–0.5 mm, very soft.
distal leaf sheaths persistent or disintegrating, yellowish to pale brown, sometimes mottled or wholly red-brown, membranaous to papery, apex acute to narrowly obtuse.
distal leaf sheaths persistent or disintegrating, colorless, stramineous or green, spotted red-brown to purple, membranous, apex narrowly acute.
basal spikelets absent; usually proliferous, ovoid to ellipsoid to linear or terete, 3.3–9.6 × 1.2–2.3 mm, apex acute;
proximal scale empty, persistent, amplexicaulous, similar to floral scales (usually slightly longer, midrib broadly green);
subproximal scale with a flower;
floral scales spiraled, 5–25, 4–8 per mm of rachilla, pale brown, usually spotted, streaked or mottled red-brown to purple, midribs green or green and red-brown, elliptic to obovate, 1.8–2.7 × 1–1.5 mm, membranous to chartaceous (papery), midrib evident to prominent, apex rounded to obtuse.
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 5–6, red-brown (proximally often white), shorter than to equaling tubercle, rarely longer, 0.9–1.3(–2) mm;
spinules sparse, retrorse, sharply acute;
stamens 3;
anthers yellow, 0.8–1.8 mm;
styles 3-fid.
perianth absent;
stamens 1;
anthers 0.2–0.3 mm;
styles 3-fid.
gray or greenish, obovoid or obpyriform, trigonous, angles very prominent, 0.6–0.9 × 0.55–0.8 mm, apex constricted proximal to tubercle, finely honeycomb-reticulate at 10–20X, each face with 20 or more rows of evident enlarged cells.
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.
whitish, gray, brown, or greenish black, pyramidal, trigonous, 0.2–0.5 × 0.4–0.5 mm.
white, gray or pale brown, pyramidal or umbonate, trigonous, 0.1–0.15 × 0.15–0.2 mm.
Eleocharis vivipara
Eleocharis nigrescens
Most specimens of Eleocharis vivipara are from Florida. Identification of vegetative (often aquatic) specimens is sometimes tentative. Eleocharis vivipara is often confused with E. microcarpa and E. brittonii, and sometimes with E. baldwinii. The red-spotted band at the sheath apex and the gray, cancellate achenes are characteristic of E. vivipara.
(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.)
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