Eleocharis interstincta |
Eleocharis obtusetrigona |
|
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knotted spikerush |
spikerush |
|
Habit | Plants perennial; rhizomes 2–4 mm thick, firm, longer internodes 3–7.5 cm, scales 5 mm, tubers absent. | Plants perennial; rhizomes 3–4 mm thick, soft to hard, longer internodes 3–8 cm, scales more than 1 cm, tubers absent. |
Culms | 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. |
obscurely 3–5-angled to terete, 40–110 cm × (2–)3.6–7.5 mm, soft, not septate-nodulose, internally spongy, transverse septa incomplete; plants never forming filiform, flaccid culms. |
Leaves | distal leaf sheaths persistent, membranous to thinly papery, apex acute to acuminate. |
distal leaf sheaths persistent, membranous, apex acute to long-acuminate, sometimes prolonged into a slender bladelike portion to 6 cm. |
Spikelets | 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. |
not proliferous, 12–43 × 3.5–6 mm; rachilla joints bearing obscure winglike remnants of floral scales; proximal scale without a flower, amplexicaulous, 3.6–7.5 mm; floral scales 30–125, 1–3 per mm of rachilla, greenish to pale brown, often with pale to dark brown submarginal band or a subapical darker spot, ovate to oblong, 4.3–5.8 × 2.5–3.3 mm, cartilaginous, often membranous toward margins, margins broadly translucent, membranous, apex rounded to acute. |
Flowers | 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. |
perianth bristles 6–7, stramineous, margins and spinules reddish to pale brown, stout, flattened, subequal, exceeding achene, 2.5–3.2 mm, coarsely retrorsely spinulose; anthers reddish brown, 1.5–1.9 mm; styles 3-fid or sometimes 2-fid. |
Achenes | 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. |
pale brown, biconvex, obpyriform, 1.7–2.3 × 1.2–1.5 mm, clearly sculptured at 10–15X, each face with 10–15 rows of transversely elongated cells, often isodiametric at achene base, apex usually constricted to neck 0.5–0.6 mm wide. |
Tubercles | dark brown, lamelliform, slightly higher than wide, 0.7–1.1 × 0.5–0.7 mm. |
stramineous, lamelliform to high-pyramidal, 0.8–1.1 × 0.7–0.9 mm. |
Eleocharis interstincta |
Eleocharis obtusetrigona |
|
Phenology | Fruiting late spring–winter. | Fruiting spring–fall. |
Habitat | Fresh ponds, lakeshores, marshes, springs, ditches, canals | Fresh, permanent water in ditches |
Elevation | 10–500 m (0–1600 ft) | 0–20 m (0–100 ft) |
Distribution |
FL; OK; TX; Mexico; Central America; e South America
|
TX; e Mexico; South America; Central America (Nicaragua) |
Discussion | 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.) |
In North America Eleocharis obtusetrigona is known from only five collections, two of them originally identified as E. fistulosa (Poiret) Link [= E. acutangula (Roxburgh) Schultes], which is common in Mexico and South America. The original description of E. obtusetrigona is poor and does not clearly distinguish E. obtusangula from E. acutangula. H. K. Svenson (1939) included E. obtusetrigona in E. acutangula, which can be distinguished by its acutely trigonous culms as well as its smaller floral scales and achenes. The tubercles are often spongy as in E. quadrangulata. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 23, p. 119. | FNA vol. 23, p. 118. |
Parent taxa | Cyperaceae > Eleocharis > subg. Limnochloa | Cyperaceae > Eleocharis > subg. Limnochloa |
Sibling taxa | ||
Synonyms | Scirpus interstinctus | Limnochloa obtusetrigona, E. fistulosa var. obtusetrigona, E. mutata var. obtusetrigona |
Name authority | (Vahl) Roemer & Schultes: in J. J. Roemer et al., Syst. Veg. 2: 149. (1817) | (Lindley & Nees) Steudel: Syn. Pl. Glumac. 2: 80. (1855) |
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