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 sedges, with fibrous roots, slender leafy stems and ovoid or oblong, many-flowered terete spikelets in terminal and axillary, mostly compound umbels, the rays and raylets bracted at the base. Scales of the spikelets spirally imbricated all around, membranous, deciduous. Flowers perfect. Perianth none. Stamens 1 or 2. Style 2-cleft, enlarged at the base. Achene lenticular or biconvex, smooth or transversely wrinkled, capped by the persistent base of the style (tubercle), or nearly the whole style persistent as a beak. [Greek, referring to the absence of perianth-bristles.]
Achene strongly wrinkled, much longer than the subacute tubercle.
Achene smooth or but little wrinkled; tubercle subulate.
P. rhynchosporoides Torr. Ann. Lye. N. Y. 3: 361. 1836.
Rhynchospora nitens A. Gray, Man. Ed. 5, 568. 1867.
Psilocarya nitens Wood, Bot. & Fl. 364. 1870.
Glabrous, culms tufted, slightly angled, 3-20 tall. Leaves narrowly linear, about 1" wide, smooth, sometimes overtopping the culm, sheathing at the base, the midvein prominent; umbels mostly loose; spikelets ovoid, 2"-3' long, rather less than 1" in diameter; scales brown, broadly ovate, thin, 1-nerved, obtuse, acute or apiculate; achene lenticular, nearly orbicular, light brown, strongly wrinkled transversely; tubercle shorter than the achene, subacute, 2-lobed at the base.
In wet soil, Long Island, N. Y., Cape May, N. J., and Delaware to Florida and Texas, near the coast, and in Indiana. July-Oct.
P. scirpoides Torr. Ann. Lye. N. Y. 3: 360. 1836.
Rhynchospora scirpoides A. Gray, Man. Ed. 5, 568. 1867.
Similar to the preceding species but smaller, usually less than'10 high. Umbels commonly more numerous; spikelets oblong or ovoid-oblong; achene nearly orbicular in outline, biconvex, not as flat as that of P. nitens, dark brown, faintly transversely wrinkled or smooth, sometimes longitudinally striate, slightly contracted at the base into a short stipe; tubercle subulate, as long as or sometimes longer than the achene, its base decurrent on the edges.
In wet soil, eastern Massachusetts, Rhode Island and northern Indiana. Perhaps a race of the preceding species. July-Sept.