Eleocharis robbinsii |
Eleocharis pachycarpa |
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Robbin's sppike-rush, Robbins' spikerush, Robbins' spikesedge, éléocharide Robbins |
black sand spikerush, broad fruit spikerush |
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Habit | Plants perennial; rhizomes (0.5–)1–2 mm thick, longer internodes 2–3 cm, scales 5–7 mm; tubers sometimes present, apical, ovoid, 4–8 × 3–4 mm. | Plants perennial, forming dense clumps, often stoloniferous. |
Rhizomes | present, caudexlike, mostly concealed by crowded culms, vertical or ascending, 2 mm thick; internodes very short, scales disintegrating to fibers, 4 mm, papery. |
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Culms | acutely trigonous; spikelet-bearing culms 16–70 cm × 0.7–0.9 mm; when submersed plants often forming numerous, filiform, flaccid culms without spikelets, sometimes with whorls of slender branches, 0.1–0.3 mm wide; soft, sometimes septate-nodulose when aquatic, internally spongy, transverse septa incomplete. |
erect to ascending or arching, acutely quadrangular, deeply sulcate, 7–50 cm × 0.3–0.5 mm, smooth, firm. |
Leaves | distal leaf sheaths persistent or decaying, membranous, apex obtuse to acuminate. |
distal leaf sheaths persistent, proximally brown or reddish, distally stramineous to green, thickly membranous, apex acute or subacute. |
Spikelets | sometimes proliferous (when submerged), 9–33 × 1.5–3 mm; rachilla joints bearing prominent winglike remnants of floral scales; proximal scale with a flower, amplexicaulous, (5–)6–9.8 mm; floral scales 4–18, 0.5–1 per mm of rachilla, stramineous to pale brown, often minutely dotted reddish, without or rarely with darker submarginal band, narrowly ovate to lanceolate, 5–7.8 × 2–3 mm, thickly papery, membranous toward margins, apex narrowly rounded to acute. |
basal spikelets absent; often proliferous, ovoid, terete, 3–10 × 2–3 mm, apex acute; proximal scale empty, amplexicaulous, similar to floral scales; subproximal scale with a flower; floral scales spiraled, 8–15, 4 per mm of rachilla, orange-brown, midrib region broadly stramineous or like flanks, ovate, 2–3 × 1.2–2 mm, membranous, midrib evident to prominent, apex acute (to rounded). |
Flowers | perianth bristles 6–7, stramineous to reddish brown, proximally slightly flattened, subequal to equal, much exceeding to rarely shorter than achene, 3–5 mm, retrorsely spinulose; anthers yellow to reddish, 1.6–3.2 mm; styles 3-fid. |
perianth bristles 6 or fewer, stramineous, unequal, some or most equaling achene, spinules obscure, sparse, retrorse, sharply acute. |
Stamens | 3; anthers 1.2–1.5 mm. |
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Styles | 3-fid. |
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Achenes | stramineous or medium brown, biconvex or compressed trigonous, narrowly obpyriform, 1.9–2.6 × 1–1.4 mm, adaxial face with 15–22 rows of rectangular, transversely elongated or nearly isodiametric cells, clearly sculptured at 10–15X, apex usually conspicuously constricted to short neck 0.4–0.7 mm wide, usually wider at tubercle base. |
stramineous, broadly obpyriform, equilaterally trigonous, angles evident, blunt, 0.9–1.1 × 0.7–0.9 mm, apex nearly truncate, smooth or obscurely papillose or rugulose at 20X. |
Tubercles | stramineous to medium brown, high-pyramidal, 0.5–1.1 × 0.3–0.7 mm. |
stramineous, pyramidal, trigonous, usually acute, proximally trilobed, the lobes decurrent on achene, 0.5–0.9 × 0.7–0.9 mm. |
Eleocharis robbinsii |
Eleocharis pachycarpa |
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Phenology | Fruiting late spring–late fall. | Fruiting late spring–summer. |
Habitat | Shallow waters of fresh lakes and ponds with sandy-peaty soils | Fresh shores, streambeds, groundwater seeps |
Elevation | 10–500 m (0–1600 ft) | 100–1400 m (300–4600 ft) |
Distribution |
AL; CT; DE; FL; GA; MA; ME; MI; MN; NC; NH; NJ; OH; SC; VA; WI; NB; NS; ON; QC
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CA; NV; South America (Argentina, Chile) [Introduced in North America; introduced in Australia]
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Discussion | I have not seen voucher specimens for literature reports of Eleocharis robbinsii from Indiana, Pennsylvania, or Rhode Island. Plants from South Carolina with the achene surface cells nearly isodiametric, the achene apex spongy, and the anthers to 3.2 mm may represent an undescribed taxon. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
H. K. Svenson (1957) placed Eleocharis pachycarpa in ser. Sulcatae Svenson. Contrary to his statement that perianth bristles are often lacking, they are present in all of the specimens we have seen. Superficially similar to E. bolanderi, from which it may readily be distinguished by its oblique leaf sheath summits, 4-angled culms, pyramidal tubercles, and often proliferating spikelets. The earliest North American specimen we have seen was collected in 1919 in Tuolumne County, California. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 23, p. 117. | FNA vol. 23, p. 91. |
Parent taxa | Cyperaceae > Eleocharis > subg. Limnochloa | Cyperaceae > Eleocharis > subg. Eleocharis > sect. Eleocharis > ser. Tenuissimae |
Sibling taxa | ||
Name authority | Oakes: Mag. Hort. Bot. 7: 178. (1841) | E. Desvaux: in C. Gay, Fl. Chil. 6: 174. (1853) |
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