Vascular Plants of North Carolina
Account for Illinois Pondweed - Potamogeton illinoensis   Morong
Members of Potamogetonaceae:
Members of Potamogeton with account distribution info or public map:
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Section 5 » Order Najadales » Family Potamogetonaceae
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AuthorMorong
DistributionKnown only from two counties (Dare and Brunswick) along the coast. These are the same counties as reported in RAB (1968), and thus no new county records have been added in over 50 years.

This is a widespread species across the continent, found from southern Canada south to southern FL and most of TX. However, there are few records in most of the Southeastern states other than FL.
AbundanceKnown from several large populations in the Buxton area of Hatteras Island in Dare County; historical now from Brunswick County. The NCNHP database has 5 records, with 3 still extant and in good to excellent condition. This is a State Endangered species.
HabitatThis is a species of interdune ponds, marshes, and impoundments. As it occurs only coastally, the waters are somewhat high in pH owing to being located in marly substrates. However, no records yet are from tidal waters of bays and estuaries.
PhenologyFlowers and fruits from May to September.
IdentificationThis is a fairly robust pondweed with large/broad submerged leaves, as compared with most others in the genus. It has a stout stem that can reach 4-6 feet long, with much branching below the water surface. The submerged leaves are elliptical to variously lanceolate or oblanceolate, about 5-6 inches long and 1.5-2 inches wide, with 11-19 nerves. The floating leaves -- usually but not always present -- are quite large as well, broadly elliptical and about 4 inches long and 1.5-2 inches wide. These leaves have quite stout petioles, about 3-4-inch long, almost as long as the leaves. These leaves tend to be dark green and shiny, often with a pale midrib (central nerve). The spikes are dense and cylindrical, about 1-1.5 inches long and 2/5-inch wide. P. nodosus is quite similar, but it has very long petioles on the submerged leaves, up to 5 inches long, and these leaves do not have sharp-pointed leaf tips. P. illinoensis has its submerged leaves sessile or on rather short petioles, and its leaves have quite sharply-pointed tips.
Taxonomic CommentsNone

Other Common Name(s)Shining Pondweed
State RankS1
Global RankG5
State StatusE
US Status
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B.A. SorrieDare County, 2012, Cape Hatteras NS, Open Water Pond W of Buxton. DareBILPhoto_natural
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