Eleocharis interstincta
Eleocharis subg. Limnochloa
knotted spikerush
present, creeping, sometimes with apical tubers.
terete, 45–100 cm × (3.2–)5–9.4 mm, soft to firm, sometimes septate-nodulose proximally, not distally, internally hollow with complete transverse septa, closer together near the spikelet, evident externally;
plants never forming filiform, flaccid culms.
16–115 cm × 0.5–8.5 mm, spongy with transverse septa incomplete or often hollow with complete transverse septa.
distal leaf sheaths persistent, membranous to thinly papery, apex acute to acuminate.
not proliferous, (20–)40–62 × 4–7 mm;
rachilla joints bearing prominent wing-like remnants of floral scales;
proximal scale empty, amplexicaulous, (3–)3.5–5 mm;
floral scales 115–220, 1–3 per mm of rachilla, stramineous to pale brown, usually with pale to dark brown submarginal band, midrib region sometimes greenish, obovate to broadly oblong, (4–)4.5–5 × 2.8–4 mm, cartilaginous, often membranous toward margins, margins broadly translucent, membranous, apex rounded to subacute.
cylindric to narrowly ellipsoid, terete, often as wide as their culms, (6–)9–75 mm;
rachilla with proximal internodes about the same thickness and length as internodes in middle of spikelet;
proximal scale empty or rarely subtending a flower;
floral scales ca. 4–220 per spikelet, spiraled, 3–8 mm, with 15 or more prominent to obscure, close, longitudinal veins, papery to cartilaginous.
perianth bristles 6–8, stramineous, stout, flattened, subequal, exceeding achene, to 2.9 mm, coarsely spinulose;
anthers stramineous to reddish, 2.5–5 mm;
styles 2-fid or 3-fid.
3-fid, or 3-fid and 2-fid.
stramineous to golden-yellow or reddish brown or gray, obovoid to obpyriform, biconvex or nearly plano-convex, often with abaxial longitudinal ridge, 1.4–1.8(–2) × 1.1–1.4 mm, markedly sculptured at 10–15X, each face with 23–37 rows of transversely elongated cells, the longitudinal walls separating the cells often prominent, apex with short neck 0.7–0.8 mm wide.
biconvex, sometimes compressed trigonous, sometimes distally constricted into a distinct, thick neck, 1.4–3 mm, markedly (to obscurely) sculptured, each face usually with 10–40 longitudinal rows of enlarged cells, sometimes nearly smooth.
dark brown, lamelliform, slightly higher than wide, 0.7–1.1 × 0.5–0.7 mm.
distinct from achenes in color, texture and form, or sometimes merging with achene apex, often dorsoventrally greatly compressed.
Eleocharis interstincta
Eleocharis subg. Limnochloa
Contrary to statements in the literature, sectioning reveals that the culm septa are closer together near the spikelet than in the rest of the culm in both Eleocharis interstincta and E. equisetoides.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Species ca. 21 (7 in the flora).
Eleocharis dulcis (Burman f.) Trinius, the Chinese water-chestnut, is sometimes cultivated in the southeastern United States for the edible tubers produced by some cultivars. According to D. B. Ward and E. M. Leigh (1976), it is also occasionally grown as an aquarium or fish-pond novelty; it apparently does not persist or escape. Because E. dulcis is a widely distributed aquatic weed in Asia, it might escape from cultivation in North America as well. It is most similar to E. interstincta and E. equisetoides; it has completely smooth achenes. Eleocharis fistulosa (Poiret) Link (= E. acutangula (Roxburgh) Schultes) was cited from North America by H. K. Svenson (1957) and D. S. Correll and H. B. Correll (1972) on the basis of Runyon’s specimens from Texas, which belong to E. obtusetrigona (Lindley & Nees) Steudel.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key to the species of Eleocharis subg. Limnochloa
1. Spikelets 1.4–3 mm wide, with 4–26 floral scales; submersed plants often forming flaccid culms without spikelets. | → 2 |
1. Spikelets 3–8 mm wide, with 30–220 floral scales; plants never forming flaccid culms without spikelets. | → 3 |
2. Achenes 0.65–1.3 × 0.5–0.8 mm; floral scales with (rarely without) conspicuous brown to blackish submarginal band. | E. elongata |
2. Achenes 1.9–2.6 × 1–1.4 mm; floral scales without (rarely with) conspicuous submarginal band. | E. robbinsii |
3. Culms hollow, with complete transverse septa (mostly evident externally). | → 4 |
3. Culms internally spongy, with incomplete transverse septa. | → 5 |
4. Achenes markedly sculptured, the longitudinal rows of enlarged cells clearly rectangular, separated by distinct longitudinal lines; perianth bristles broad and stout, exceeding achene; culms smooth or sometimes septate-nodulose proximally. | E. interstincta |
4. Achenes obscurely sculptured, sometimes partially smooth, the longitudinal rows of enlarged cells linear, separated by obscure longitudinal lines; perianth bristles narrow and weak, rudimentary to equaling achene; culms septate-nodulose through out. | E. equisetoides |
5. Culms clearly acutely 4 angled. | E. quadrangulata |
5. Culms terete or obscurely 3–5-angled. | → 6 |
6. Floral scales broadly suborbicular; tubercles 0.1–0.5 × 0.2–0.5 mm, confluent with or narrower than achene apex; achene apex narrowed into stout spongy region; perianth bristles smooth or rarely finely spinulose. | E. cellulosa |
6. Floral scales ovate to oblong; tubercles 0.8–1.1 × 0.7–0.9 mm, proximally wider than achene apex; achene apex without stout spongy region; perianth bristles coarsely spinulose. | E. obtusetrigona |
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