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Key to Scirpus

Cyperaceae

Scirpus

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1 Bristles smooth, without teeth along the margins, strongly contorted and greatly exceeding the achenes when extended.
  2 Scales usually with prominent green midribs; mature bristles mostly contained within the scales; achenes 1.0-1.3 mm long, brown to purplish-brown when mature.
    3 Perianth bristles (extended) shorter than, equal to, or slightly exceeding the achene; mature culms lax, the inflorescences lopping over to (or nearly to) the ground, with 2-3 lateral inflorescences in addition to the terminal one; rays of the inflorescence scabrous throughout their lengths, ascending to divergent, with axillary bulblets
    3 Perianth bristles (extended) exceeding the achene by 2-3×; mature culms rigid, nearly upright, with 0-2 lateral inflorescences in addition to the terminal one; rays of the inflorescence glabrous for most of their lengths (moderately scabrous toward outer end), ascending, lacking axillary bulblets
  2 Scales usually with inconspicuous midribs; mature bristles exceeding the scales and giving the inflorescence a woolly appearance; achenes 0.6-1.0 mm long, whitish, pale, brown, dark brown or black.
      4 Plants colonial by elongate rhizomes; scales 2-3.1 mm long; achenes reddish-brown; [NJ northwards]
      4 Plants cespitose in tussocks; scales 1.1-2.2 mm long; achenes tan to whitish; [collectively widespread].
        5 Achenes maturing Aug-Sep; spikelets in dense cymes of 2-15, the central spikelet sessile, the others either sessile or pedicellate; [widespread]
        5 Achenes maturing Jun-Jul; spikelets in open cymes, the central spikelet sessile, the others pedicellate; [NJ, PA, WV, OH, and KY northwards].
          6 Achenes maturing late Jun to early Jul; scales usually blackish, at least toward the tip; involucral bracts solid black at base; leaves 2-5 mm wide; [WV northwards]
          6 Achenes maturing Jul; scales pale brown (rarely some black along the midrib); involucral bracts brownish at base (sometimes bordered with black); [n. NJ, OH, c. KY, and MO northward]
1 Bristles with retrorse or antrorse teeth along the margins, strongly contorted to nearly straight, shorter than to greatly exceeding the achenes when extended (or bristles absent or nearly so in S. georgianus).
             7 Spikelets all solitary with distinct pedicels; mature scales with broad green midribs; achenes with protruding angles and concave sides
             7 Spikelets all or mostly in glomerules with the pedicels scarcely developed; mature scales with midribs not usually green; achenes less sharply trigonous, the sides convex, flat, or slightly concave.
               8 Culms with 10-20 leaves; spikelets broadly ovate; scales reddish-brown and, excluding the tips, about as wide as long
               8 Culms with 2-10 leaves; spikelets broadly ovate to narrowly ovate; scales brown or black and, excluding the tips, mostly longer than wide.
                 9 Bristle teeth thick-walled and sharp-pointed, densely arranged almost to the base of the bristle.
                   10 Plants cespitose with short, brownish rhizomes; leaf sheaths green throughout; scales broadest above the middle; achenes 0.6-0.8 mm wide
                   10 Plants spreading with long, reddish rhizomes having conspicuous nodes and internodes; lower leaf sheaths red-tinged near their bases; scales usually broadest below the middle; achenes (0.6-) 0.8-1.0 mm wide.
                     11 Styles 3-cleft; achenes trigonous, with poorly-developed receptacles from which the bristles readily detach; bristles (3-) 6; upper part of culm usually scabrous; [widespread]
                     11 Styles 2 (-3)-cleft; achenes biconvex with well-developed receptacles with persistent bristles; bristles 4 (-5); upper part of culm usually smooth; [from NJ, WV, and KY northward]
                 9 Bristle teeth thin-walled and with rounded tips, mostly restricted to the upper 2/3 of the bristle (or bristles absent or nearly so in S. georgianus).
                       12 Bristles 0-3, shorter than the achenes; teeth, if present, concentrated near the tips of the bristles
                       12 Bristles usually 5-6, shorter than to slightly longer than the achenes; teeth extending basally from the tips of all or at least some of the bristles.
                          13 Scales 1.6-2.8 mm long, terminating in a flattened or terete awn 0.4-0.6 (1.2) mm long
                          13 Scales 1.0-2.1 mm long, terminating in a mucro 0.1-0.3 (-0.4) mm long.
                            14 Mature culms lax and reclining with the inflorescences lopping over to (or nearly to) the ground; glomerules usually with < 15 spikelets; lower scales of spikelets slightly mucronate, blackish
                            14 Mature culms upright or nearly so; glomerules frequently with > 15 spikelets; lower scales of spikelets mucronate, blackish or brownish.
                              15 Lower leaf blades and sheaths usually nodose-septate; spikelets ovate or narrowly ovate; scales mostly brownish; longer bristles frequently exceeding the achenes; achenes 1.0-1.3 mm long
                              15 Lower leaf blades and sheaths nearly smooth; spikelets broadly ovate or ovate; scales mostly blackish; longer bristles usually shorter than or about equaling the achenes; achenes 0.8-1.1 mm long