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 or perennial sedges. Culms in our species simple, triangular, leafy near the base, and with 1 or more leaves at the summit, forming an involucre to the simple or compound, umbellate or capitate inflorescence. Rays of the umbel sheathed at the base, usually very unequal, one or more of the heads or spikes commonly sessile. Spikelets flat or subterete, composed of few or many scales, the scales falling away from the wingless or winged rachis as they mature (nos. 1-23), or persistent and the spikelets falling away from the axis of the head or spike with the scales attached (nos. 24-37). Scales concave, conduplicate or keeled, 2-ranked, all flower-bearing or the lower 1 or 2 empty. Flowers perfect. Perianth none. Stamens 1-3. Style 2-3-cleft, deciduous from the summit of the lenticular or 3-angled achene. [Ancient Greek name for these sedges.]
About 600 species, widely distributed in tropical and temperate regions. Besides the following, some 50 others occur in the southern United States. The English names. Galingale or Galangal and Sweet Rush are sometimes applied to all the species. Type species: Cyperus esculentus L.
*Style 2-cleft; achene lenticular, not 3-angled; scales falling from the rachis; spikelets flat.
Achene one-half as long as the scale; umbel nearly or quite simple.
Spikelets yellow; superficial cells of the achene oblong.
Spikelets green or brown; superficial cells of the achene quadrate.
Scales obtuse or obtusish, appressed.
Scales membranous, dull; style much exserted.
Scales subcoriaceous, shining; style scarcely exserted.
Scales acute, somewhat spreading at maturity.
Achene narrowly obovate; spikelets 1/2- 1 1/2' long.
Achene linear-oblong; spikelets 3 "-9" long.
Scales ovate, brownish; umbel usually subcapitate.
Scales oblong-lanceolate, greenish; umbel usually loose.
Achene nearly as long as the scale; umbel sometimes much compound.
** Style 3-cleft; achene 3-angled.
Scales falling away from the persistent rachis of the flattened spikelets.
Wings of the rachis. if present, permanently adnate to it.
Scales tipped with recurved awns; low annual, 1'-6' tall.
Scales acute or obtuse, not awned.
Wings of the rachis none or very narrow.
Stamens 2 or 3; spikelets linear-oblong, 2 1/2"-12" long.
Annual; culms smooth, 2'-2o' long.
Scales sharply acuminate.
Scales blunt, mucronulate.
Perennial; culms 1°-2 1/2° tall.
Heads oblong; spikelets erect or ascending; culms rough.
Heads short; spikelets more or less spreading; culms smooth.
Scales broadly ovate; achene 1" long.
Scales oblong-ovate; achene 1 1/4" long.
Stamen 1; spikelets ovate, 2"-4" long.
Tall perennial; achene linear; scales acutish.
Low annual; achene oblong; scale-tips recurved.
Wings of the rachis distinct.
Low annual, adventive from Europe; scales brown.
Tall indigenous perennials (no. 17 sometimes annual?).
Lower leaves reduced to pointed sheaths.
Leaves all elongated-linear.
Scales mucronate, reddish brown or green.
Scales acute or obtuse, not mucronate.
Scales wholly or partly purple-brown; achene linear.
Scales tightly appressed.
Tips of the scales free.
Scales straw-colored; achene obovoid.
Wings of the rachis separating from it as interior scales; annuals.
Spikes loose; spikelets 3"-10" long.
Spikes dense, cylindric; spikelets 1 1/2"-2l/2" long.
Spikelets falling away from the axis of the spikes, the lower pair of scales commonly persistent.
Annuals; spikelets elongated, nearly terete.
Scales imbricated or but slightly distant; achene obovoid.
Scales thin, dull brown; spikelets slender.
Scales rigid, yellow-brown; spikelets stout.
Scales very distant; achene linear-oblong; spikelets very slender.
Perennial by hard, tuber-like basal corms, spikelets more or less flattened.
Achene narrowly linear-oblong, 3-4 times as long as thick.
Spikelets flat, several-many-flowered.
Spikelets subterete, few-flowered.
Spikelets 6"-12" long, loosely spicate, the lower reflexed.
Spikelets 1 1/2"-6" long, densely capitate or spicate.
Spikelets all reflexed; culms rough.
Spikelets spreading or obovoid, the lower reflexed; culms smooth.
Heads oblong or cylindric.
Spikelets 2"-5" long, at least the lower reflexed.
Head oblong or short-cylindric; lower spikelets reflexed.
Head obovoid; all but the upper spikelets reflexed.
Spikelets 1 l/2"-2" long, the lower spreading.
Achene oblong or obovoid, about twice as long as thick.
Rachis wingless or very narrowly winged.
Rachis-wings membranous, broad.
Scales firm, not appressed; spikelets loosely capitate.
Scales thin, closely appressed; spikelets densely capitate.