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Key to Juncus, KEY D: Subkey in Juncus

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1 Leaves flattened, narrowly elliptic in cross-section.
  2 Leaves with incomplete septae; heads about 10 mm diameter; tips of dehisced capsules united; [subgenus Juncus, section Iridifolii]
  2 Leaves with complete septae; heads about 12 mm diameter; tips of dehisced capsules split; [subgenus Juncus, section Ozophyllum]
1 Leaves terete, not at all flattened; [subgenus Juncus, section Ozophyllum].
    3 Plants strictly cespitose, without any short, hard, knotty rhizomes; tepals lanceolate
    3 Plants with at least some short, hard, knotty rhizomes; tepals lanceolate-subulate.
      4 Capsules shorter than the tepals, clearly included within the tepals at maturity
      4 Capsules equaling or exceeding the tepals, exserted from or only barely included within the tepals at maturity.
        5 Capsule valves separating at the apex at maturity; stamens 6.
          6 Heads 6-20 flowered, 6-9 mm diameter; auricles cartilaginous, 0.5-1.0 mm long
          6 Heads 25-100 flowered, 10-14 mm diameter; auricles membranous, 2.5-4.0 mm long
        5 Capsule valves remaining united at the apex after dehiscence; stamens 3.
             7 Culms 4-8 mm in diameter near the base, usually > 80 cm tall; inflorescences usually > 15 cm tall, with > 25 heads; largest leaf blades > 25 cm long and > 3 mm in diameter
             7 Culms 1-3 mm in diameter near the base, usually < 80 cm tall; inflorescences usually < 10 cm tall, with < 25 heads; largest leaf blades < 25 cm long and 1-2 mm in diameter.
               8 Uppermost cauline leaf blade much shorter than its sheath; tepals reddish to reddish brown; outer tepals significantly longer than the inner tepals; basal leaf sheaths and cataphylls deep reddish purple
               8 Uppermost cauline leaf blade equaling or longer than its sheath; tepals green to straw-colored; outer tepals and inner tepals of similar length; basal leaf sheaths and cataphylls straw-colored to brown.
                 9 Heads lobulate; mature capsule 2.0-3.0 mm long
                 9 Heads spherical, not lobulate; mature capsule 3.0-4.5 mm long

Key to Juncus, KEY E: Subkey in Juncus

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1 Mature capsules 2 mm or more longer than the perianth, 4.0-5.2 mm long
1 Mature capsules < 1.5 mm longer than the perianth, or subequal to it.
  2 Stamens 6.
    3 Proximal culm leaf overtopping inflorescence; culms well spaced along creeping rhizomes; plants often exceed 8 dm tall; [northeastern, south to DE, MD, disjuncts in ne. NC]
    3 Proximal culm leaf shorter than inflorescence; plants cespitose; plants < 8 dm tall; [collectively widespread].
      4 Mature capsules slightly shorter than to slightly longer than the perianth (< 0.5 mm longer); perianth 2.6-3.9 mm long; inflorescence 4-16 cm long; [widespread]
      4 Mature capsules exceeding the perianth by about 1 mm (> 0.5 mm longer); perianth 1.6-3.0 mm long; inflorescence 2-11 cm long; [northern or montane in our region].
        5 Capsule apices acute (rarely obtuse); inner tepals acute to acuminate; inflorescence branches widely ascending to spreading
        5 Capsule apices rounded or obtuse, mucronate; inner tepals acute to obtuse; inflorescence branches strictly ascending
          6 Tepals rounded, ca. half the length of the capsules; 6-10 flowers per glomerule; the inflorescence length similar to its width (or only slightly exceeding)
          6 Tepals (at least the outer 3) acute, ± same length as the capsules (or slightly shorter); 3-5 (-12) flowers per glomerule; the inflorescence length much exceeding its width
  2 Stamens 3.
             7 Mature capsules about 1/3 longer than perianth (roughly 1-1.5 mm longer)
             7 Mature capsules equaling or barely exceeding perianth.
               8 Heads 1-50; capsules 2.4-3.6 mm long
                 9 Perennial, capsules 2.8-3.6 mm long, tepals 2.6-3.6 mm long; [widespread in our area]
                 9 Annual, capsules 2.4-2.5 mm long, tepals 1.9-2.3 mm long; [endemic to the Altamaha Grit, Coastal Plain of GA]
               8 Heads 30-250; capsules 1.9-2.9 mm long.
                   10 Capsules deep chestnut brown; roots with terminal tubers; inner tepals usually > 2.4 mm long; [southeastern]
                   10 Capsules straw colored; roots without terminal tubers; inner tepals usually 1.7-2.3 mm long; [midwestern, east to w. Panhandle FL and se. TN]