Contains 10 accepted taxa overall.

Characteristics
Potamogeton L.
PONDWEED
Classification
ALISMATALES
Potamogeton
Citation
POTAMOGETON Linnaeus, Sp. Pl. 126. 1753.
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TYPE: Potamogeton natans Linnaeus Lectotypified by Taylor, in Britton, N. Amer. Fl. 17(1): 14, 30. 1909.
Species
Scientific Name Common Name Herbarium Specimens Status Photos
Potamogeton crispus CURLY PONDWEED Not Native OBL (NWPL)
Potamogeton diversifolius WATERTHREAD PONDWEED Native OBL (NWPL)
Potamogeton epihydrus RIBBONLEAF PONDWEED Native OBL (NWPL)
Potamogeton floridanus FLORIDA PONDWEED Native Endemic Endangered-State OBL (NWPL)
Potamogeton foliosus LEAFY PONDWEED Native OBL (NWPL)
Potamogeton illinoensis ILLINOIS PONDWEED Native OBL (NWPL)
Potamogeton nodosus LONGLEAF PONDWEED Native OBL (NWPL)
Potamogeton perfoliatus CLASPINGLEAF PONDWEED Native OBL (NWPL)
Potamogeton pulcher SPOTTED PONDWEED Native OBL (NWPL)
Potamogeton pusillus SMALL PONDWEED Native OBL (NWPL)
Identification Key
1.  Submersed leaf blade filiform, linear, or ribbon-like, 0.1-10 mm wide
2
1.  Submersed leaf blades broadly linear-oblong, lanceolate, elliptic, to nearly orbiculate, 3-58 mm wide (occasional stranded plants without submersed leaves)
7
2.  Rhizomes present; floating leaves present, at least in some plants in population
3
2.  Rhizomes absent; floating leaves absent
5
3.  Lacunae absent in submersed leaves
3.  Lacunae prominent in submersed leaves
4
4.  Stipular sheaths of submersed leaves adnate to base of leaf blade, tip projecting as ligule; submersed leaf blades to 2 mm wide; floating leaf blades 0.8-1.6 cm long; submersed peduncle axillary and recurved, emersed axillary or terminal and erect to slightly recurved; submersed spike capitate, 2-3 mm long, emersed cylindric, 5-9.7 mm long; fruit lateral wings with sharp points …
4.  Stipular sheaths of submersed leaves free from base of leaf blade or with only 1/–5 sheath adnate, ligule not obvious; submersed leaf blades 1-10 mm wide; floating leaf blades 2-8 cm long; peduncle axillary, erect; spike cylindric, 8-40 mm long; fruit with lateral keels lacking sharp points
5.  Fruits with abaxial keel or ridge; turions common; peduncle 0.3-1.1(3.7) cm long; embryo with 1 full spiral
5.  Fruits with abaxial surface rounded; turions uncommon; peduncle 0.5-6.6 cm long; embryo with <1 full spiral
6
6.  Leaf blade with 0-2 rows of lacunae along midrib, apex acute, rarely apiculate, rarely with bristle; stipules connate; peduncles filiform to cylindric, 1-3 per plant; inflorescences interrupted; mature fruits obovoid, sides concave, beak toward adaxial edge, rarely median …
6.  Leaf blade with 1-5 rows of lacunae along midrib, apex acute to obtuse; stipules convolute; peduncles cylindric, more than 3 per plant; inflorescences continuous; mature fruits widest at middle or ovoid, sides rounded, beak median, not toward adaxial edge
7.  Stem flattened; leaves mostly submersed (sometimes floating or stranded), blade margins conspicuously serrate; fruit beak 2–3 mm; turions formed, hard
7.  Stem terete; leaves only submersed (in P. perfoliatus) or submersed and emergent, blade margins entire; fruit beak 1 mm or less; turions rarely formed
8
8.  Submersed leaves clasping stem; floating leaves absent (leaves sometimes at the surface or stranded)
8.  Submersed leaves petiolate or sessile (not clasping); floating leaves present
9
9.  Stem conspicuously rusty- or black-spotted; floating leaf blade 1.2-3.2 times as long as wide, 1.5-5 cm wide, rounded to cordate at base; submersed leaf blades crispate, mostly arcuate
9.  Stems without conspicuous dark spots; floating leaf blade 2.2-11 times as long as wide, rounded-acute to cuneate at base, usually tapering to petiole, 1-3 cm wide; submersed leaf blades flat or crispate, mostly not arcuate or occasionally arcuate
10
10.  Submersed leaves sessile or petioles 0.1-4 cm long, the petioles usually shorter than the blade; larger submersed leaves acuminate; fruits grayish green to olive-green
10.  Submersed leaves with petioles (0.5)2-13 cm long, the petioles usually subequal to longer than the blade; larger submersed leaves acute at apex; fruits red to reddish brown
Genus Synonyms
Synonym Full Citation Basionym Type
Spirillus Spirillus J. Gay, Compt. Rend. Hebd. Seances Acad. Sci. 38: 703. 1854. TYPE: Non designatus.