Eleocharis engelmannii |
Eleocharis nigrescens |
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Engelman spikerush, Engelmann's spike-rush, Engelmann's spikesedge, englemann's spike-rush |
black spikerush |
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Habit | Plants usually annual, tufted, not stoloniferous; rhizomes absent. | |
Culms | 2–40 cm × 0.5–1.5(–2) mm. |
sometimes ascending, subterete, elliptic, or polygonal, (1–)3–7.5(–9) cm × 0.2–0.5 mm, very soft. |
Leaves | apex of distal leaf sheath obtuse to acute, tooth to 0.3 mm. |
distal leaf sheaths persistent or disintegrating, colorless, stramineous or green, spotted red-brown to purple, membranous, apex narrowly acute. |
Spikelets | lanceoloid to subcylindric or ovoid, 5–10(–20) × 2–3(–4) mm, apex acute (to rounded); proximal scale empty, encircling ca. 2/3 of culm; floral scales 25–100(–200), 8–12 per mm of rachilla, orangebrown to stramineous, 2(–2.5) × 1–1.3 mm, midribs mostly keeled, ovate, apex narrowly rounded to subacute. |
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. |
Flowers | perianth bristles present or often absent, 5–8, brown, stout, rudimentary to slightly exceeding tubercle; stamens (2–)3; anthers brown to yellow, 0.3–0.7(–1) mm; styles 2–3-fid. |
perianth absent; stamens 1; anthers 0.2–0.3 mm; styles 3-fid. |
Achenes | 0.9–1.1(–1.5) × 0.7–1.1 mm. |
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. |
Tubercles | depressed, subdeltoid, 0.1–0.3(–0.4) × 0.6–0.9(–1) mm, 1/10–2/5 as high as wide, 1/4 or less as high as achene, 9/10 as wide as achene, very rarely 2/5 as high as achene (in E. engelmannii var. robusta). |
white, gray or pale brown, pyramidal or umbonate, trigonous, 0.1–0.15 × 0.15–0.2 mm. |
2n | = 10. |
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Eleocharis engelmannii |
Eleocharis nigrescens |
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Phenology | Fruiting spring–fall. | Fruiting summer–winter. |
Habitat | Fresh shores, marshes, disturbed places | Moist terrestrial sites such as sandy and peaty soils on pond margins, ditches, pine flatwoods |
Elevation | 30–2400 m (100–7900 ft) | 0–30 m (0–100 ft) |
Distribution |
AL; AR; AZ; CA; CO; CT; DC; DE; IA; ID; IL; IN; KS; KY; MA; MD; MI; MN; MO; MS; MT; ND; NE; NH; NJ; NM; NY; OH; OK; OR; PA; RI; TN; TX; VA; WA; WI; WV; AB; BC; MB; ON
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FL; SC; Mexico; South America; West Indies; Bermuda; Africa |
Discussion | Robust plants known only from Missouri and described as Eleocharis engelmannii var. robusta have well-developed caudices, culms to 2 mm wide (pressed), spikelets to 2 cm, floral scales to 2.5 mm and slightly cartilaginous, styles mostly trifid, achenes to 1.5 × 1 mm, and tubercles 0.3–0.5 × 0.7–1 mm and to 2/5 as high as achene. Some specimens are intermediate between E. engelmannii and E. obtusa, or rarely with E. lanceolata. I have not seen specimens to verify literature reports of E. engelmannii from Manitoba, Connecticut, Delaware, Idaho, New Hampshire, North Carolina, Oregon, Rhode Island, South Carolina, South Dakota, or Vermont. (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.) |
Source | FNA vol. 23, p. 104. | FNA vol. 23, p. 93. |
Parent taxa | Cyperaceae > Eleocharis > subg. Eleocharis > sect. Eleogenus > ser. Ovatae | Cyperaceae > Eleocharis > subg. Eleocharis > sect. Eleocharis > ser. Tenuissimae |
Sibling taxa | ||
Synonyms | E. engelmannii var. detonsa, E. engelmannii var. monticola, E. engelmannii var. robusta, E. monticola, E. monticola var. leviseta, E. ovata var. detonsa | Scirpidium nigrescens |
Name authority | Steudel: Syn. Pl. Glumac. 2: 79. (1855) | (Nees) Steudel: Syn. Pl. Glumac. 2: 77. (1854) |
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