Eleocharis robbinsii Oakes

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.

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. 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. Leaves: distal leaf sheaths persistent or decaying, membranous, apex obtuse to acuminate. 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. 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. 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. Tubercles stramineous to medium brown, high-pyramidal, 0.5–1.1 × 0.3–0.7 mm.

N.B., N.S., Ont., Que.; Ala., Conn., Del., Fla., Ga., Maine, Mass., Mich., Minn., N.H., N.J., N.C., Ohio, S.C., Va., Wis.

Fruiting late spring–late fall.

Shallow waters of fresh lakes and ponds with sandy-peaty soils; 10–500m.

Eleocharis robbinsii Oakes, Mag. Hort. Bot 7:178. 1841.
Culms slender, 1-2 mm. wide, 2-7 dm. high, triangular, sometimes producing tufts of capillary stems which float in the water ; roots either fibrous or spongy ; stolons slender and elongate, the nodes inconspicuous; sheaths dull brown, the summit oblique; spikelet 1-2.5 cm. long, acute, scarcely wider than the culm; scales few (4-9), lanceolate, 7 mm. long, greenish, striate, the margins and tip scarious, with a keel formed by 2 or 3 prominent longitudinal ridges; style trifid; stamens 3; achenes brown, 2-2.5 mm. long (not including the slender, elongate style-base), oblong-obovate, narrowed below the middle, lenticular, rarely triangular, turgid, with 15-18 rows of shallow, transversely linear-rectangular cells, narrowed at the apex to a neck one-half the width of the achene, broadening again to form the base of the flattened style ; bristles 7, closely and firmly toothed, twice as long as the achene.
Type locality :Pondicherry Pond, Jefferson, New Hampshire (Robbins).
Distribution : Shallow water, borders of ponds and in ditches : chiefly along the coast. Nova nTl^ and Ne^Y Brunswick to North Carolina, Georgia, and northern Florida; inland also in yuebec (Vtctorin), New York, Pennsylvania, Indiana, Michigan, Wisconsin, and Ontario
f r^n'^lX!^™''^^'^,?J^h ^^"■,^^^•.^ ^^^f2^0; Britt. & Brown, 111. Fl. ed. 2. 1: 311. /. 760; Rhodora 31 : pi. 188, f. 5; Rep. N. J. Mus. 1910: pi. 17 f 7