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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. |
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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). |
11 Stipules fibrous, often whitish. |
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 bristle-tipped (rarely apiculate); peduncles recurved, axillary or axillary and terminal, 0.5-6.6 cm long |
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 |