Vascular Plants of North Carolina
Account for Longleaf Pondweed - Potamogeton nodosus   Poiret
Members of Potamogeton with account distribution info or public map:
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Section 5 » Order Najadales » Family Potamogetonaceae
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DistributionWidely scattered over the state, with SERNEC showing records from nine counties in the state. A distinct pattern of distribution is not clear, though most records are from Coastal Plain counties.

This is a very widespread species across North America, from southern Canada south to northern FL, southern TX, and all of CA.
AbundanceVery rare to rare. The NCNHP database has only 4 records, none current. The SERNEC database (January 2020) lists only Harnett and Stanly counties with collections post-1990. This is important, as the NCNHP has a State Rank of SH (historical), as does Weakley (2018) on his map. However, VA has several dozen records in SERNEC (some of them recent), as does SC. The website editors thus feel that the species is certainly extant in the state, and suggest a State Rank of S1?. This is a Significantly Rare species.
HabitatThis is a species of still to slow-moving waters of ponds, lakes, streams, and rivers. Waters can often be rather deep, up to nearly 6' deep.
See also Habitat Account for General Herbaceous Ponds
PhenologyFlowers and fruits from May to September.
IdentificationThis is a robust species of pondweed, with a potentially tall stature (underwater), reaching to 5-6 feet long, and highly branched. The submersed leaves are quite thin but large, with the blades from 4-6 inches long and about 3/4-inch wide, narrowly elliptical in shape, but with the blade tip not sharp-tipped (as in P. illinoensis). The blade has 7-15 nerves. The petioles of these leaves are very long, often 4-5 inches long. The normally present floating leaves are large, as well, about 3-4 inches long and 1 inch wide, elliptical; their petioles are also quite long, up to 6 inches long. The spikes are dense, rather large at 1.5-2 inches long, and cylindrical in shape; they are normally conspicuous above the water surface, being held erectly or ascending. As mentioned above, P. illinoensis, limited in NC to just a few coastal impoundments, is quite similar but has the submerged leaves with a distinctly sharp tip to the leaves.
Taxonomic CommentsNone

Other Common Name(s)Knotty Pondweed, American Pondweed, Loddon Pondweed
State RankSH [S1?]
Global RankG5
State StatusSR-D
US Status
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