This pondweed was first collected in New York in 1886 in Cayuga Lake near Ithaca but it has not been seen there since. The specific name honors the Reverend E.J. Hill who discovered it in Michigan in 1880. This plant is considered rare in every state/province where it is known.
There are 21 known populations of this globally rare plant in New York. There are three unverifed reports from the 1980s and about a dozen historical locations that need to be surveyed. Most of these populations are likely threatened to some degree from run-off, aquatic herbicide application, motor boat activities, or other activities that reduce water quality.
Populations can fluctuate wildly in numbers from year-to-year so it is very difficult to establish a short-term trend although a few populations have disappeared entirely.
This plant seems to have declined in the Finger Lakes area but new populations have been found elsewhere in the state so overall numbers are stable.
There is a low threat from surrounding development of water bodies and the use of aquatic herbicides. Most of the present populations have no protection from these threats.
In order to better protect known populations, any application of an aquatic herbicide should carefully consider the impacts on this globally rare plant. Any efforts to protect lands within the watershed where this pondweed is present should be encouraged. At a minimum, the hydrological integrity for known sites should be maintained.
Research needs to be done into the causes of large fluctuations in plant numbers within populations. We need to know how these plants react to disturbance and herbicide use.
An aquatic plant of alkaline waterways including ponds, streams, lakes, ditches, and other impoundments. Typically habitat is present along I-90 near the Massachusetts border where ineffective culverts have created shallow impoundments over calcareous bedrock. Recorded water level varies from exposed muddy substrate to 2.5 meters. When water is deeper, the plants scarcely reach the surface (New York Natural Heritage Program 2004). Alkaline waters of marshes, ponds, lakes, and slow-moving streams (Flora of North America 2000). Chiefly in clear, cold, calcareous waters (Gleason and Cronquist 1991). Highly alkaline ponds and streams (Hellquist and Crow 1980).
This aquatic plant is generally found in the calcareous wetlands and ponds of the eastern Hudson Valley and central New York. New populations have recently been found in eastern Jefferson County and along the upper Hudson River. New York is near the southern edge of its range.
Potamogeton hillii occurs in Vermont, Massachusetts, Connecticut, New York, Pennsylvania, Ohio, Michigan, Wisconsin, and Ontario.
This is an aquatic plant with masses of long, very narrow leaves visible just below the surface of waters with a high pH. There are 9-15 veins running the length of the leaf. There are one or two rows of large open cells on either side of the midvein and a very pointed little bristle at the tip of the leaf.
The leaves of this aquatic plant are linear, with the primary leaves 1-2.2 mm broad, sharply acute and cuspidate, usually bristle-tipped or long apiculate, and 3-nerved. The midrib is usually bordered by 1 or 2 rows of lacunae. The stipules are free, whitish, 0.8-1.8 cm long, and sharply acute with strong persistent fibers. The peduncles are clavate and 0.5-1.5 cm long. The spike is capitate and 5-8 mm in diameter. The fruits are 3-3.6 mm long, 2.3-3 mm broad, and 3-keeled with a prominent dorsal keel. The ventral margin of the fruit is rounded to a short recurved beak.
This plant can be identified vegetatively, but the presence of fruits makes it easier to run through the identification keys. If found, a specimen with leaves and preferably with mature fruit should be collected and carefully pressed to show the leaves and stipules.
Potamogeton hillii is an easily recognized species either in fruit or when sterile. The leaf blade has a bristle tip and five or fewer veins. Those characters combined with the usual absence of nodal glands will separate this species from all other North American linear-leaved species. Ecologically, it is consistently found in more alkaline waters than any other North American pondweed (Flora of North America 2000). Leafy pondweed (Potamogeton foliosus) has an acute leaf tip that may have a small mucronate or apiculate tip, but it is not bristle-tipped.
Vegetative plants of this aquatic species are present from late spring to early fall. The ideal survey period is mid-June to early September.
The time of year you would expect to find Hill's Pondweed vegetative and fruiting in New York.
Potamogeton hillii Morong
Crow, Garrett E. and C. Barre Hellquist. 2000. Aquatic and Wetland Plants of Northeastern North America: A revised and enlarged edition of Norman C. Fassett's a Manual of Aquatic Plants. Volume One: Pteridophytes, Gymnosperms, and Angiosperms: Dicotyledons. The University of Wisconsin Press. Madison, Wisconsin. 536 Pages.
Fernald, M.L. 1950. Gray's manual of botany. 8th edition. D. Van Nostrand, New York. 1632 pp.
Flora of North America Editorial Committee. 2000. Flora of North America north of Mexico. Vol. 22. Magnoliophyta: Alismatidae, Arecidae, Commelinidae (in part), and Zingiberidae. Oxford Univ. Press, New York. xxiii + 352 pp.
Gleason, Henry A. and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York. 910 pp.
Haynes, R.R. 1974. A Revision of North American Potamogeton Subsection Pusillii (Potamogetonaceae). Rhodora 76: 564-649.
Hellquist, C.B. 1984. Observations of Potamogeton hillii Morong in North America. Rhodora 86: 101-111.
Hellquist, C.B. and G.E. Crow 1980. Aquatic Vascular Plants of New England: Part 1. Zosteraceae, Potamogetonaceae, Zannichelliaceae, Najadaceae. New Hampshire Agricultural Experiment Station University of New Hampshire. Station Bull. 515.
Holmgren, Noel. 1998. The Illustrated Companion to Gleason and Cronquist's Manual. Illustrations of the Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York.
Mitchell, Richard S. and Gordon C. Tucker. 1997. Revised Checklist of New York State Plants. Contributions to a Flora of New York State. Checklist IV. Bulletin No. 490. New York State Museum. Albany, NY. 400 pp.
New York Natural Heritage Program. 2010. Biotics database. New York Natural Heritage Program. New York State Department of Environmental Conservation. Albany, NY.
New York Natural Heritage Program. 2022. New York Natural Heritage Program Databases. Albany, NY.
Reschke, Carol. 1990. Ecological communities of New York State. New York Natural Heritage Program, New York State Department of Environmental Conservation. Latham, NY. 96 pp. plus xi.
Weldy, T. and D. Werier. 2010. New York flora atlas. [S.M. Landry, K.N. Campbell, and L.D. Mabe (original application development), Florida Center for Community Design and Research http://www.fccdr.usf.edu/. University of South Florida http://www.usf.edu/]. New York Flora Association http://newyork.plantatlas.usf.edu/, Albany, New York
Information for this guide was last updated on: February 15, 2005
Please cite this page as:
New York Natural Heritage Program. 2022. Online Conservation Guide for Potamogeton hillii. Available from: https://guides.nynhp.org/hills-pondweed/. Accessed July 2, 2022.