This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Annual, similar to the preceding species, but culms commonly taller, sometimes 18' high. Upper sheath obliquely truncate or 1-toothed; spikelet oblong-cylindric or ovoid-cylindric, obtuse or subacute, 2"-8" long, 1"-1 1/2" in diameter, many-flowered; scales pale brown with a green midvein and narrow scarious margin, ovate, obtuse, deciduous; style 2-cleft; bristles about 6, not longer than the achene, or wanting; achene broadly obovate, brown, smooth, lenticular; tubercle broad, low, covering the top of the achene.
In wet soil, Massachusetts to Indiana, South Dakota, Washington, New Jersey, Texas and California. July-Sept.
E. macrostachya Britton; Small, Fl. SE. U. S. 184. 1903.
Perennial by rootstocks, pale green. Culms tufted, rather stout, sometimes twisted, 40 high or less; spikelet lanceolate-cylindric, about 1" long or less, acute, many-flowered; scales oblong-ovate to oblong-lanceolate, acute, light green to . straw-color, with a somewhat darker midvein; bristles as long as the achene and tubercle, or shorter, sometimes very short; style 2-cleft; achene obovate, lenticular, 1.5 mm. long, brown, the cap-like tubercle small, yellow.
In wet soil, Missouri to Louisiana, Nevada, California and Jalisco. Aug.-Sept.
Perennial by horizontal rootstocks, culms stout or slender, terete or somewhat compressed, striate, 1 1/2°-5° tall. Basal sheaths brown, rarely bearing a short blade, the upper one obliquely truncate; spikelet oblong to ovoid-cylindric, 3"-12" long, 1 1/2"-2" in diameter, many-flowered, thicker than the culm; scales ovate-oblong or ovate-lanceolate, purplish-brown with scarious margin and a green midvein, or pale green all over; bristles usually 4, slender, retrorsely barbed, longer - than the achene and tubercle, sometimes wanting; stamens 2-3; style 2-3-cleft; achene lenticular, smooth, yellow, over 1/2" long; tubercle conic-triangular, constricted at the base, flattened, one-fourth to one-half as long as the achene.
In ponds, swamps and marshes, Labrador to British Columbia, south to Florida, Texas and California. The species consists of many races, the culms slender to stout, the tubercle narrow or quite broad. Also in Europe and Asia. Aglet-headed rush. Aug.-Sept.