Part 7 - UNC Herbarium

POTAMOGETONACEAE 930
2 Submersed leaves petioled or sessile, not clasping the stem; floating leaves absent or present.
5 Submersed leaves 19-49 veined, distinctly arcuate ...............................................................................P. amplifolius
5 Submersed leaves with fewer than 29 veins, not arcuate.
6 Stems conspicuously black-spotted; submersed leaves crisped along the margin; floating leaves 15-21 veined
........................................................................................................................................................... P. pulcher
6 Stems inconspicuously spotted or lacking spots; submersed leaves flat along the margin; floating leaves 7-29
veined.
7 Submersed leaves with petioles 1-13 cm long.
8 Larger submersed leaves acute at the apex with a sharp awl-like tip; fruit gray-green to olive-green,
with well-developed lateral ridges.................................................................................. P. illinoensis
8 Larger submersed leaves acute at the apex but lacking a sharp awl-like tip; fruit red to reddishbrown,
with muricate lateral ridges ....................................................................................P. nodosus
7 Submersed leaves sessile.
9 Stipules blunt; submersed leaves 7 veined; fruit plump, stalked, tawny-olive.................. [P. alpinus]
9 Stipules acute; submersed leaves 3-19 veined; fruit laterally compressed, not stalked, reddishbrown,
gray-green, or olive-green.
10 Fruit reddish-brown, with obsolete or rounded keel; submersed leaves with (3-) 5-9 veins........
................................................................................................................................P. gramineus
10 Fruit gray-green or olive-green, with well-developed keel; submersed leaves with 7-19 veins ..
................................................................................................................................ P. illinoensis
Key C
1 Fruit with a prominent keel 0.2-1.2 mm broad; floating leaves often present; lacunae prominent in submersed leaves.
2 Submersed leaves 3-13 veined; stipules of submersed leaves not adnate to the leaf base; floating leaves rounded at apex
........................................................................................................................................................................P. epihydrus
2 Submersed leaves 1-3 (-7) veined; stipules of at least some submersed leaves adnate to the leaf base; floating leaves
acute at apex................................................................................................................................................P. tenneseensis
1 Fruit with a keel < 0.2 mm broad; floating leaves absent or present; lacunae present in some species, but generally not
prominent.
3 Floating leaves present, at least in some plants of the population.
4 Floating leaves 0.3-1.6 cm long; peduncle 0.6-1.5 cm long; fruit < 2.5 mm long...................................... [P. vaseyi]
4 Floating leaves 1.5-12 cm long; peduncle 2.5-3.5 mm long; fruit 2.5-5 mm long.
5 Petiole junction with leaf distinctly pale in color; floating leaves ovate, oblong-ovate, cordate at base, rarely
tapering ................................................................................................................................................P. natans
5 Petiole junction with leaf lacking pale color; floating leaves elliptical, ovate-elliptical, or oblong-ellliptical.
6 Floating leaves 7-12 mm wide, tapering at both ends; fruit apparently not produced ......... [P. floridanus]
6 Floating leaves 10-20 (-30) mm wide, obtuse, round or tapering at the base; fruit often produced.............
..............................................................................................................................................P. oakesianus
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............................. P. confervoides
7 Rhizomes absent or not apparent; peduncle 0.3-7 cm long, often curved; leaves usually not thread-like, 0.1-5 mm
wide.
8 Nodal glands absent.
9 Leaves 15-35 veined, > 2 mm wide; stem conspicuously flattened; peduncles terminal, usually straight...
...........................................................................................................................................P. zosteriformis
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; fruits 1-keeled, 1.4-2.3 (-2.7) mm long............
....................................................................................................................... P. foliosus var. foliosus
10 Leaves usually bristle-tipped, occasionally apiculate to blunt, 3 veined, 1-2.2 (-4) mm wide; fruits
3-keeled, 2.3-4 mm long.......................................................................................................... P. hillii
8 Nodal glands present.
11 Stipules fibrous, often whitish.
12 Leaf apex acute or apiculate; leaves 5-7 (-9) veined; turions with inner leaves at a right angle to
outer leaves..........................................................................................................................[P. friesii]
12 Leaf apex usually bristle-tipped, acute or rarely obtuse to apiculate; leaves 3-5 (-7) veined; turions
flattened with inner and outer leaves in same plane ......................................................P. strictifolius
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........................................................................................................................ P. hillii
13 Leaf apex blunt, acute, or apiculate, but not bristle-tipped; peduncles straight, terminal, 0.5-6.6 cm
long.