1 Main involucral bracts 2-8, spreading and foliaceous (the inflorescence thus appearing terminal); rhizomes bearing ovoid tubers; bristles persistent on the achene; achenes 2.5-5 mm long (including body and apiculus)

1 Main involucral bract 1 (rarely with an additional 1-2 lateral bracts), erect and terete or triangular, appearing as a continuation of the culm (the inflorescence thus appearing lateral, though in some species the longer inflorescence branches may overtop the bract); rhizomes not bearing tubers; bristles falling from the achene; achenes 1.0-4.5 mm long (including body and apiculus).

  2 Spikelets on stalks of varying lengths, at least some clearly not sessile.

    3 Culms distinctly triangular in cross-section, more sharply so above than below, nearly terete near the base; [section Malacogeton]

    3 Culms terete throughout, or obscurely triangular above; [section Schoenoplectus].

      4 Culms firm, not easily compressed; scales 3-4 mm long.

        5 Achenes biconvex (or rarely weakly trigonous), styles 2; spikelets 3-190, usually in clusters of 2-8 on pedicels, sometimes solitary, but never all solitary throughout inflorescence; bristles usually 6 (5-7), of equitant or differing lengths; scales usually with copious red-brown dots

        5 Achenes trigonous, styles 3; spikelets 5-30, mostly solitary or rarely 2 together borne on the same pedicels; bristles 4, of two conspicuous lengths; scales without copious red-brown dots (sometimes obscurely dotted)

      4 Culms soft and spongy, easily compressible; scales (2.0-) 2.5-3.0 (-3.5) mm long.

          6 Perianth bristles retrorsely barbed; spikelets obtuse; culms terete throughout their length

  2 Spikelets all sessile, in a cluster at one point (rarely with 1 or 2 short branches to 5 mm long).

             7 Spikelet solitary; leaves numerous; plant usually aquatic, the culms and leaves flaccid, supported by the water; [section Malacogeton]

             7 Spikelets (1-) 2-several; leaves 1-4; usually of wet places, but the culms stiff and erect, not floating.

               8 Cespitose annual or perennial; culms terete (or acutely triangular in Schoenoplectiella mucronata), 1-6 dm tall

               8 Rhizomatous perennial; culms triangular in cross-section, usually 5-20 dm tall.

                 9 Leaves elongate, > ½ as long as the culms; achenes trigonous; styles 3-branched; [section Malacogeton]

                 9 Leaves short, < ½ as long as the culms; achenes plano-convex; styles 2 (-3) branched; [Schoenoplectus pungens complex of section Schoenoplectus].

                   10 Sides of the culm strongly concave, wing-angled; culms 3-10 mm in diameter; main involucral bract 1-2.5 (-6) cm long; spikelet scale with apical notch 0.1-0.4 mm deep

                   10 Sides of the culm flat, slightly concave, or slightly convex; culms 1-6 mm in diameter; main involucral bract (1-) 3-20 cm long; spikelet scale with apical notch (0.3-) 0.5-1 mm deep.

                     11 Spikelets 3-35; achenes 1.9-2.6 mm long, biconvex; styles 2-fid

                     11 Spikelets 1-5 (-10); achenes (2.0-) 2.5-3.5 mm long, biconvex or trigonous; styles 2-3-fid.

                       12 Styles 3-fid; achenes thickly lenticular to bluntly trigonous; spikelet scales brown to tan

                       12 Styles 2-fid; achenes lenticular; spikelet scales brown