Eleocharis parvula |
Eleocharis obtusetrigona |
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dwarf spikerush, dwarf spikesedge, little-head spike-rush, little-head spikesedge, small spike-rush, éléocharide naine |
spikerush |
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Habit | Plants perennial; rhizomes 3–4 mm thick, soft to hard, longer internodes 3–8 cm, scales more than 1 cm, tubers absent. | |
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. |
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Leaves | distal leaf sheaths persistent, membranous, apex acute to long-acuminate, sometimes prolonged into a slender bladelike portion to 6 cm. |
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Spikelets | 2–4 × 1–2 mm, sometimes absent in deeper water; proximal scale 1/2 or more of spikelet length; floral scales 6–10 per spikelet, 1.4–2.7 mm, commonly entirely stramineous, 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, stramineous, fairly stout to slender, usually equaling achene to slightly exceeding tubercle, sometimes unequal and some 1/2 of achene, very rarely rudimentary, minutely retrorsely spinulose; anthers 0.7–1.2 mm. |
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, sometimes pale brown, obovoid to obpyriform, thickly trigonous, angles distinct, faces concave to plane, rarely convex, 0.9–1.2 × 0.55–0.75 mm, apex tapered, smooth or faintly rough at 30X. |
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. |
Tubers | terminating rhizomes usually markedly J- or horseshoe-shaped, body (apart from apical bud) oblong, 2–2.5(–5) × 0.5–1 mm; tubers among culm bases straight, narrowly fusiform, 4–5 mm. |
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Tubercles | 0.1–0.2 × 0.15 mm. |
stramineous, lamelliform to high-pyramidal, 0.8–1.1 × 0.7–0.9 mm. |
2n | = 10 (Europe). |
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Eleocharis parvula |
Eleocharis obtusetrigona |
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Phenology | Fruiting summer–fall (north) or late winter–fall (far south). | Fruiting spring–fall. |
Habitat | Brackish or saline, mostly coastal tidal marshes, shores, mud flats, swamps, ponds, ditches | Fresh, permanent water in ditches |
Elevation | 0–600 m (0–2000 ft) | 0–20 m (0–100 ft) |
Distribution |
AL; AR; CA; CT; FL; GA; IL; IN; KS; LA; MA; MD; ME; MI; MO; MS; NC; NJ; NY; OH; OR; SC; VA; WA; BC; NB; NL; NS; QC; Mexico; Central America (Nicaragua); Eurasia
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TX; e Mexico; South America; Central America (Nicaragua) |
Discussion | Plants without well-developed bristles are otherwise typical Eleocharis parvula. S.-O. Strandhede and R. M. T. Dahlgren (1968) provided a detailed description from Scandinavia; the mostly curved tubers of North American plants are differently shaped than the ovoid, mostly nearly straight tubers illustrated by them. Eleocharis parvula is very uncommon inland. Plants lacking spikelets and having rather broad culms with evident aerenchyma (E. parvula forma spongiosa Fassett) that are submerged in tidal zones closely resemble small plants of Sagittaria graminea. Eleocharis parvula has also been reported from North Dakota, South America, and Africa; I have not seen specimens. Plants without achenes or tubers cannot be reliably identified to species. Literature reports from Cuba, Mexico, and Venezuela may be based on specimens of E. coloradoensis. (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. 106. | FNA vol. 23, p. 118. |
Parent taxa | Cyperaceae > Eleocharis > subg. Eleocharis > sect. Parvulae | Cyperaceae > Eleocharis > subg. Limnochloa |
Sibling taxa | ||
Synonyms | Scirpus parvulus, E. pygmaea, S. nanus | Limnochloa obtusetrigona, E. fistulosa var. obtusetrigona, E. mutata var. obtusetrigona |
Name authority | (Roemer & Schultes) Link ex Bluff Nees: Comp. Fl. German. ed. 2, 1: 93. (1836) | (Lindley & Nees) Steudel: Syn. Pl. Glumac. 2: 80. (1855) |
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