Eleocharis quadrangulata (Michx.) Roem. & Schult.

We have not seen voucher specimens for the reports of Eleocharis quadrangulata from Kansas. Plants with greenish achenes, longer bristles, and longer anthers than the average are known from Tennessee.

The tubercles of Eleocharis quadrangulata are often spongy as in E. obtusetrigona.

Plants perennial; rhizomes 1.5–4 mm thick, soft to hard, longer internodes 3–8 cm, scales 5–10 mm, tubers absent. Culms acutely quadrangular, (30–)45–105 cm × (1–)2–5.4 mm, soft to firm, internally spongy, transverse septa incomplete; plants never forming filiform, flaccid culms. Leaves: distal leaf sheaths persistent, membranous, apex narrowly acute to acuminate, sometimes prolonged into a bladelike portion to 8 cm. Spikelets not proliferous, (15–)20–76 × 3–5(–6) mm; rachilla joints bearing obscure winglike remnants of floral scales; proximal scale empty, amplexicaulous, (1–)2.2–5.4 mm; floral scales (28–)45–135, 2–3 per mm of rachilla, stramineous to pale brown, usually with pale to dark brown submarginal band, midrib region sometimes greenish, broadly obovate to ovate, (4–)4.5–6.2 × 2.8–5 mm, subcartilaginous, apex rounded to obtuse. Flowers: perianth bristles 6–7, whitish to brown, slender, often markedly unequal, shorter than achene or some equalling tubercle, sparsely retrorsely spinulose to smooth; anthers stramineous to red-brown, 2.3–2.9 mm; styles 3-fid, sometimes 2-fid. Achenes yellow or pale green to brown or purplish, biconvex, obovoid to obpyriform, 1.8–3 × 1.3–2 mm, almost smooth to markedly sculptured at 10–15X, each face with 19–38 rows of almost linear, transversely elongated cells, which are sometimes isodiametric at achene base, apex often constricted to neck 0.3–0.4 mm wide. Tubercles dark brown or whitish, deltoid to high-pyramidal or lanceoloid, 0.7–1.5 × 0.4–1 mm, often spongy.

Ont.; Ark., Calif., Conn., Del., Fla., Ga., Ill., Ind., Ky., La., Mass., Mich., Miss., Mo., N.J., N.Y., N.C., Ohio, Okla., Oreg., Pa., S.C., Tex., Va., W.Va., Wis.; s to c Mexico.

Fruiting early summer–winter.

Shallow water of fresh lake and pond shores, marshes; 10–600m.

Scirpus quadrangulatus Michaux, Fl. Bor.-Amer. 1: 30. 1803; Eleocharis quadrangulata var. crassior Fernald; Scirpus albomarginatus Schultes; S. marginatus Muhlenberg

Eleocharis quadrangulata (Michx.) R. & S Syst. Veg. 2: 155. 1817.
Scirpus quadrangulatus Michx. Fl. Bor.-Am. 1: 30. 1803.
Scirpus marginatus Muhl. Descr. Gram. 28. 1817. Not S. marginatus Thunb. 1794. Scirpus albo marginatus Schultes in R. & S. Syst. Veg. Mant. 2: 74. 1824.
Eleocharis quadrangulata var. crassior Fernald, Rhodora 37 : 393. 1935. (Wellcsley, Massachusetts.)
Culms 4-sided, with sharp angles, coarse, 5-10 dm. high, from a short caudex; roots coarse, gray, often tuber-bearing; sheaths red or brown, membranous, with a loose, brown tip, glistening, sometimes prolonged into leaf-like blades; spikclets 2-5 cm. long, cylindric, acute ; scales 4-ranked, elliptic, 5 mm. long, 2 mm. wide, rounded or somewhat acute, strawcolored, striate, not keeled ; style bifid or trifid ; stamens 3 ; achene 2.7-4.2 mm. long including the beak (1 mm. long), narrowly obovate, deep shining-brown, almost smooth, with about 24 rows of transverse linear cells, narrowed at the summit to a neck about one-fourth the width of the achene, broadening again to form the base of the elongated triangular style ; bristles light brown, equaling the achene, slender and obscurely toothed.
Type locality: Carolina (the slender typical plant).
Distribution : Deep to shallow water : Massachusetts, west to Wisconsin, south to Texas ; Jalisco.

Eleocharis quadrangulata is a species of spikesedge known by the common names square-stem spikerush and four-angled spikerush. It is native to eastern and central North America (from Texas and Florida north to Ontario and Massachusetts), with additional populations in California, Oregon, and west-central Mexico (Durango, Jalisco, etc.). It grows in and around freshwater in lakes, ponds, and other bodies of water. It is a rhizomatous perennial herb growing one half to one meter in height. The spongy, compressible stem is a few millimeters wide and sharply four-angled. The inflorescence is a single spikelet 1.5 to 7.5 centimeters long which is made up of several flowers covered in light brown bracts.

Eleocharis quadrangulata là loài thực vật có hoa trong họ Cói. Loài này được (Michx.) Roem. & Schult. mô tả khoa học đầu tiên năm 1817.