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..
Leafy sedges, mostly perennial by rootstocks, with erect 3-angled or terete culms, narrow flat or involute leaves, and ovoid oblong or fusiform, variously clustered spikelets. Scales thin, i-nerved, imbricated all around, usually mucronate by the excurrent midvein, the lower empty. Upper flowers imperfect, the lower perfect. Perianth of 1-20 (mostly 6) upwardly or downwardly barbed or scabrous bristles, wanting in some species (no. 2). Stamens commonly 3. Style 2-cleft, 2-toothed or rarely entire. Achene lenticular or swollen, not 3-angled, smooth or transversely wrinkled, capped by the persistent base of the style (tubercle), or in some species by the whole style. [Greek, referring to the beak-like tubercle.]
Style entire or 2-toothed, persistent as a long-exserted subulate beak.
Style deeply 2-cleft, only its base persistent as a tubercle.
Bristles minute or wanting.
Bristles downwardly barbed or rarely smooth.
Scales white or nearly so; bristles 9-15.
Scales brown; bristles 6.
Leaves filiform: achene oblong.
Leaves narrowly linear, flat; achene obovate.
Bristles equalling the achene; tubercle one-half as long or less.
Bristles reaching or exceeding the end of the tubercle, which is as long as the achene.
Spikelets few-several in numerous rather loose clusters.
Spikelets very numerous in 2-6 very dense globose heads.
Bristles upwardly barbed.
Spikelets numerous in 2-6 very dense globose heads.
Spikelets few-several in rather loose clusters.
Leaves setaceous; achene obovate, shining.
Leaves narrowly linear.
Achene broadly oval.
Achene narrowly obovate.
Achene transversely wrinkled.
Spikelets ovoid, in erect cymose clusters; achene longer than the bristles.
Leaves flat; spikelets nearly or quite sessile.
Leaves involute; spikelets distinctly pedicelled.
Spikelets spindle-shaped, in drooping panicles; bristles long.