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Key to Potamogeton, Key B: pondweeds with connate leaves and submersed leaves 0.1-10 mm wide

Potamogetonaceae

Potamogeton

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1 Fruit with a prominent keel 0.2-1.2 mm broad; floating leaves often present; lacunae (thin rows of translucent tissue on each side of midrib) prominent in submersed leaves.
  2 Submersed leaves 1-10 mm wide, 3-13 veined; stipules of submersed leaves not adnate to the leaf base; floating leaves rounded at apex
  2 Submersed leaves 0.2-1(-2) mm wide, 1-3 (-7) veined; stipules of at least some submersed leaves adnate to the leaf base; floating leaves acute at apex
1 Fruit with a keel < 0.2 mm broad; floating leaves absent or present; lacunae (thin rows of translucent tissue on each side of midrib) present in some species, but generally not prominent.
    3 Floating leaves present, at least in some plants of the population (sometimes only present when plants are fertile, as in P. vaseyi).
      4 Floating leaf blade thinner (0.6-1.5 cm wide); peduncle 0.5-3 cm long; fruits 1.5-2.5 mm long
      4 Floating leaf blade wider (1.5-12 cm wide); peduncle 2.5-9.5 cm long; fruits 2.5-5 mm long.
        5 Petiole junction with leaf distinctly pale in color; floating leaves ovate, oblong-ovate, cordate at base, rarely tapering
        5 Petiole junction with leaf lacking pale color; floating leaves elliptical, ovate-elliptical, or oblong-elliptical.
          6 Floating leaves 7-12 mm wide, tapering at both ends; fruit apparently not produced
          6 Floating leaves 10-20 (-30) mm wide, obtuse, round or tapering at the base; fruit often produced
    3 Floating leaves absent from all plants in the population.
             7 Rhizomes obvious; peduncle 5-25 cm long; leaves thread-like, 0.1-0.5 mm wide
             7 Rhizomes absent or not apparent; peduncle 0.3-7 cm long, often curved; leaves usually not thread-like, 0.1-5 mm wide.
                 9 Leaves 15-35 veined, > 2 mm wide; stem conspicuously flattened; peduncles terminal, usually straight
                 9 Leaves 3-5 veined, usually < 2 mm wide; stem terete; peduncles usually axillary, recurved.
                   10 Leaves acute, 3 (-5)-veined, 0.3-1.5 (-2.3) mm wide; lacunae rarely present; fruits 1-keeled, 1.4-2.3 (-2.7) mm long
                   10 Leaves usually bristle-tipped, occasionally apiculate to blunt, 3-veined, 1-2.2 (-4) mm wide; lacunae in 1-2 rows on each side of midrib; fruits 3-keeled, 2.3-4 mm long
               8 Nodal glands present (sometimes apparently absent or inconspicuous in P. strictifolius).
                       12 Leaf apex rounded or apiculate, leaves 1.2-3.2 mm wide, 5-7(-9) veined; winter buds (turions) with leaves ca. 4 ranked, with inner (upright) leaves fanlike and at a right angle to outer leaves (those laterally disposed), the outer leaves corrugated
                       12 Leaf apex usually bristle-tipped, acute or rare obtuse to apiculate, leaves 0.6-2 mm wide, 3-5 (-7) veined; winter buds (turions) with leaves ca. 2 ranked, flattened, with inner and outer leaves in same plane (both upright, more or less in the same orientation as stem), the outer leaves not corrugated
                     11 Stipules not fibrous, usually delicate, green, brown, or white.
                          13 Leaf apex blunt, acute, or apiculate, but not bristle-tipped; peduncles straight, terminal, 0.5-6.6 cm long.
                            14 Leaves 1-3.5 mm wide, often reddish-brown colored, with rounded or slightly apiculate apices; fruits with abaxial or lateral keels; [ne. PA, n. NJ, northward]
                            14 Leaves 0.2-2.5 mm wide, usually green colored, with apices obtuse, apiculate, or acute; fruits rounded, without keels; [widespread in US, throughout our flora region].
                              15 Mature fruit mostly widest at middle, or ovate, sides rounded, beak mostly central; peduncle cylindrical, usually > 3 per plant; inflorescence continuous; leaves with 1-5 rows of lacunae along midrib, apex acute to obtuse; stipules mostly convolute
                              15 Mature fruit obovate, sides concave, beak mostly forward; peduncle filiform to cylindrical, usually 1-3 per plant; inflorescence usually interrupted; leaves with up to 2 rows of lacunae along midrib, apex acute, rarely apiculate; stipules mostly connate