Hill's Pondweed

Potamogeton hillii Morong

Potamogeton hillii
Beth Yanunk-Platt

Monocotyledoneae (Monocots)
Potamogetonaceae (Pondweed Family)
State Protection
Listed as Threatened by New York State: likely to become Endangered in the foreseeable future. For animals, taking, importation, transportation, or possession is prohibited, except under license or permit. For plants, removal or damage without the consent of the landowner is prohibited.
Federal Protection
Not Listed
State Conservation Status Rank
Imperiled or Vulnerable in New York - Very vulnerable, or vulnerable, to disappearing from New York, due to rarity or other factors; typically 6 to 80 populations or locations in New York, few individuals, restricted range, few remaining acres (or miles of stream), and/or recent and widespread declines. More information is needed to assign either S2 or S3.
Global Conservation Status Rank
Vulnerable globally - At moderate risk of extinction due to rarity or other factors; typically 80 or fewer populations or locations in the world, few individuals, restricted range, few remaining acres (or miles of stream), and/or recent and widespread declines.


Did you know?

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.

State Ranking Justification

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.

Short-term Trends

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.

Long-term Trends

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.

Conservation and Management


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.

Conservation Strategies and Management Practices

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

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).

Associated Ecological Communities

  • Deep emergent marsh (guide)
    A marsh community flooded by waters that are not subject to violent wave action. Water depths can range from 6 in to 6.6 ft (15 cm to 2 m). Water levels may fluctuate seasonally, but the substrate is rarely dry, and there is usually standing water in the fall.
  • Eutrophic dimictic lake* (guide)
    The aquatic community of a nutrient-rich lake that occurs in a broad, shallow basin. These lakes are dimictic: they have two periods of mixing or turnover (spring and fall); they are thermally stratified in the summer, and they freeze over and become inversely stratified in the winter.
  • Farm pond/artificial pond*
    The aquatic community of a small pond constructed on agricultural or residential property. These ponds are often eutrophic, and may be stocked with panfish such as bluegill and yellow perch.
  • Marl pond (guide)
    The aquatic community of a small, shallow, spring-fed pond in which the water has a high concentration of calcium. The calcium precipitates out of the water as calcium carbonate and forms a marl sediment.
  • Marsh headwater stream* (guide)
    The aquatic community of a small, marshy perennial brook with a very low gradient, slow flow rate, and cool to warm water that flows through a marsh, fen, or swamp where a stream system originates. These streams usually have clearly distinguished meanders (i.e., high sinuosity) and are in unconfined landscapes.
  • Mesotrophic dimictic lake* (guide)
    The aquatic community of a lake that is intermediate between an oligotrophic lake and a eutrophic lake. These lakes are dimictic: they have two periods of mixing or turnover (spring and fall); they are thermally stratified in the summer, and they freeze over and become inversely stratified in the winter.

* probable association but not confirmed.

Associated Species

  • Brasenia schreberi (water-shield)
  • Ceratophyllum demersum (common coon-tail)
  • Chara vulgaris
  • Elodea canadensis (Canada waterweed)
  • Lemna minor (common duckweed)
  • Ludwigia palustris (water-purslane)
  • Najas minor (eutrophic water-nymph, eutrophic naiad)
  • Potamogeton gramineus (grass-leaved pondweed)
  • Potamogeton natans (floating-leaved pondweed)
  • Potamogeton robbinsii (Robbins's pondweed, fern pondweed)
  • Sagittaria latifolia (common arrowhead)
  • Typha latifolia (wide-leaved cat-tail)
  • Utricularia cornuta (horned bladderwort)
  • Wolffia columbiana (Colombian water-meal)
  • Zosterella dubia


New York State Distribution

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.

Global Distribution

Potamogeton hillii occurs in Vermont, Massachusetts, Connecticut, New York, Pennsylvania, Ohio, Michigan, Wisconsin, and Ontario.

Identification Comments

General Description

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.

Identifying Characteristics

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.

Best Life Stage for Proper Identification

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.

Similar Species

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.

Best Time to See

Vegetative plants of this aquatic species are present from late spring to early fall. The ideal survey period is mid-June to early September.

  • Vegetative
  • Fruiting

The time of year you would expect to find Hill's Pondweed vegetative and fruiting in New York.

Hill's Pondweed Images


Hill's Pondweed
Potamogeton hillii Morong

  • Kingdom Plantae
    • Phylum Anthophyta
      • Class Monocotyledoneae (Monocots)
        • Order Najadales
          • Family Potamogetonaceae (Pondweed Family)


  • Potamogeton porteri Fernald [This taxon probably represents <i>Potamogeton hillii</i> with a wider leaf than typically encountered.]

Additional Resources

Best Identification Reference

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.

Other References

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. 2024. 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


About This Guide

Information for this guide was last updated on: February 15, 2005

Please cite this page as:
New York Natural Heritage Program. 2024. Online Conservation Guide for Potamogeton hillii. Available from: https://guides.nynhp.org/hills-pondweed/. Accessed June 21, 2024.