Eleocharis subg. Limnochloa
Ann. Lyceum Nat. Hist. New York 3: 296. 1836.
Plants perennial, when submerged sometimes with spikelets proliferating. Rhizomes present, creeping, sometimes with apical tubers. Culms 16–115 cm × 0.5–8.5 mm, spongy with transverse septa incomplete or often hollow with complete transverse septa. Spikelets 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. Styles 3-fid, or 3-fid and 2-fid. Achenes 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. Tubercles distinct from achenes in color, texture and form, or sometimes merging with achene apex, often dorsoventrally greatly compressed.
Tropical, subtropical (and warm temperate) areas worldwide.
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.
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.||Eleocharis elongata|
|2||Achenes 1.9–2.6 × 1–1.4 mm; floral scales without (rarely with) conspicuous submarginal band.||Eleocharis 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.||Eleocharis 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.||Eleocharis equisetoides|
|5||Culms clearly acutely 4 angled.||Eleocharis 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.||Eleocharis 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.||Eleocharis obtusetrigona|