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Potamogeton epihydrus

Potamogeton epihydrus is a perennial aquatic plant known by the common name ribbonleaf pondweed, Nuttall's pondweed (not to be confused with Elodea nuttallii) or in Britain and Ireland American pondweed.[2] It is native to much of North America, where it grows in water bodies such as ponds, lakes, ditches, and slow-moving streams.[3]


This is a perennial, rhizomatous herb producing narrow, compressed, unspotted stems to a maximum length of about 1 m.[3][4] The stems are either unbranched or sparingly branched.[5] It has two types of leaf. The submersed leaves are sessile 5-25 cm long and 0.1-1 cm wide, translucent, linear in shape and ribbonlike, red-brown to light green in colour with a blunt to acute tip.[3] The floating leaves are similar to the floating leaves of other Potamogeton, petiolate and opaque, up to 8 centimeters long and 3 wide.

The inflorescence is a small spike of flowers that arises from the water on a peduncle 1.5-5 (rarely up to 16) cm.[3]

This is a diploid species, with 2n = 26.[3][6] Hybrids have been described with P. gramineus, P. nodosus (P. × subsessilis Hagstrom), P. bicupulatus (P. × aemulans Z. Kaplan, Hellq. and Fehrer), and P. perfoliatus (P. × versicolor Z. Kaplan, Hellq. and Fehrer).[3][7]

Potamogeton epihydrus, whole plant. Photo: Barre Hellquist.


Potamogeton epihydrus (meaning 'on the water surface') was described by Rafinesque in 1808,[1] one of the earlier North American species to be named.

DNA analysis[8] indicates that, despite the presence of floating leaves P. epihydrus is closely related to P. tennesseensis. These two are within the basal part of the large clade of fine-leaved pondweeds including P. diversifolius, P. pusillus and P. compressus.


Ribbonleaf pondweed is predominantly a North American species, and is widespread in boreal and temperate North America. Its centre of distibution is the northeastern USA and southeastern Canada from the Atlantic to the Great Lakes, and on the Pacific seaboard from northern California to British Columbia. However, there are scattered populations in Alabama and Louisiana, Alaska, Wyoming, Montana and central Canada.[3]

There are also two isolated populations in Britain, where it was identified as recently as 1944.[9] The Outer Hebrides population is thought to be naturally occurring; there is also an accidentally introduced population in the Rochdale and Calder & Hebble Canals.[4]

Ecology and Conservation[edit]

Ribbonleaf pondweed generally grows in shallow, standing to slow-flowing standing and running waters at up to 1900 m altitude.[3] It tolerates acid waters as low as pH 5 and has a preference for oligotrophic, soft water conditions.[4][10][11] Nevertheless, liming experiments suggest that ribbonleaf pondweed is sensitive to severe acidification.[12] P. epihydrus is a poor disperser relative to many other aquatic plants occurring in Connecticut lakes.[10]

Ribbonleaf pondweed is generally common and widespread in North America.[3] However, it is listed as Endangered in Indiana and Special Concern in Tennessee.[13] In Britain it is Nationally Rare and listed as Vulnerable.[14][15] British populations lack detectable genetic variation, suggesting a strong founder effect.[16]


P. epihydrus is not in cultivation, but would be worth attempting to grow. Its fairly small size, ribbon-like underwater leaves and scattered floating leaves could be effectively used in a garden pond, tub or stream. Introduced populations in Britain have not proved invasive, so there is little chance of it becoming problematic. Like other pondweeds, it needs to be planted with the root in contact with a suitable substrate such as aquatic compost.


  1. ^ a b The Plant List: Potamogeton epihydrus. Royal Botanic Gardens, Kew and Missouri Botanic Gardens. Accessed November 18, 2014
  2. ^ "BSBI List 2007" (xls). Botanical Society of Britain and Ireland. Retrieved 2014-10-17. 
  3. ^ a b c d e f g h i Haynes R.R., Hellquist C.B. 2014. Potamogeton epihydrus. In: Flora of North America Online (
  4. ^ a b c Preston C.D. (1995). Pondweeds of Great Britain and Ireland. BSBI Handbook No. 8. Botanical Society of the British Isles, London.
  5. ^ Wiegleb G., Kaplan Z. 1998. An account of the species of Potamogeton L. Folia Geobotanica, 33, 241-316
  6. ^ Kaplan Z., Jarolímová V., Fehrer J, 2013. Revision of chromosome numbers of Potamogetonaceae: a new basis for taxonomic and evolutionary implications. Preslia, 85, 421-482.
  7. ^ Kaplan Z., Fehrer J., Hellquist C.B. 2009. New Hybrid Combinations Revealed by Molecular Analysis: The Unknown Side of North American Pondweed Diversity (Potamogeton). Systematic Botany, 34, 625-642.
  8. ^ Lindqvist C., De Laet J., Haynes R.R., Aagesen L., Keener B.R., Albert V.A. 2006. Molecular phylogenetics of an aquatic plant lineage, Potamogetonaceae. Cladistics, 22, 568-588.
  9. ^ Heslop Harrison J.W. 1950. A pondweed, new to the European flora, from the Scottish Western Isles, with some remarks on the phytogeography of the island group. Phyton Annales Rei Botanicae, Horn, 2, 104-109.
  10. ^ a b Capers R.S., Selsky R., Bugbee G.J. 2009. The relative importance of local conditions and regional processes in structuring aquatic plant communities. Freshwater Biology, 55, 952-966.
  11. ^ Pierce, J.R., Jensen M.E. 2002. A Classification of Aquatic Plant Communities Within the Northern Rocky Mountains. Western North American Naturalist, 62, 257-265.
  12. ^ Weiher E.R., Boylen C.W., Bukaveckas P.A. 1994. Alterations in Aquatic Plant Community Structure following Liming of an Acidic Adirondack Lake. Canadian Journal of Fisheries and Aquatic Sciences, 51, 20-24.
  13. ^ Plants Profile: Potamogeton epihydrus
  14. ^ Preston C.D., Pearman D.A., Dines T.D. 2014. Online Atlas of the British and Irish Flora: Potamogeton epihydrus.
  15. ^ Cheffings C.M., Farrell, L. (Eds), Dines T.D., Jones R.A., Leach S.J., McKean D.R., Pearman D.A., Preston C.D., Rumsey F.J., Taylor I. 2005. The Vascular Plant Red Data List for Great Britain. Species Status, 7, 1-116. Joint Nature Conservation Committee, Peterborough.
  16. ^ Hollingsworth P.M., Preston C.D., Gornall R.J. 1998. Lack of detectable isozyme variability in British populations of Potamogeton epihydrus (Potamogetonaceae). Aquatic Botany, 60, 433-437.


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