Introduction to the Potamogetonaceae Family

The Potamogetonaceae family is a family of exclusively aquatic plants, mostly freshwater, that provide crucial ecosystem services in aquatic environments on every continent except Antarctica.

I have known about this important family since I was a child, playing with the Potamogeton that was growing in our backyard pond. Since I love lakes, swamps, and anything aquatic, I came across it often in my youth. Now, I understand and appreciate their importance so much more.

Common Botanical Description of the Potamogetonaceae Family

If you’re new to plant morphology, this guide is a perfect beginner’s description for learning to identify the Potamogetonaceae family, with no need to know any scientific jargon. Below this section is additional information on uses and morphology photos to help you identify the family, followed by pictures of individual species found in North America. But for researchers or those wanting to learn a more in-depth version, refer to the Scientific Botanical Description below the images for highly detailed scientific descriptions and genus-level distribution data.

Leaves and Stems of the Potamogetonaceae: This family is entirely aquatic herbs from creeping rhizomes that are rooted, and they have simple (not compound) leaves that may be submerged or floating and submerged and are arranged alternately or in whorls of 3 along the stems. Leaves typically appear to have leaf-like appendages (stipules) at their base.

Flowers of the Potamogetonaceae: Flowers emerge above the water on long stalks and are usually in spike-like clusters or sometimes a simple pair of flowers. Flowers are not your typical flowers with petals; instead, they have 0-4 ‘tepals,’ depending on how they are interpreted.

Reproductive Features of the Potamogetonaceae: Each flower has 4 fertile stamens and an ovary made of 4 free chambers (carpels).

Fruits of the Potamogetonaceae: Fruits are fleshy or non-fleshy aggregate fruits, meaning they are made from several flowers to produce a fruit that may appear like a drupe (think cherry with a central pit), an achene (think sunflower seed), or berry-like in Groenlandia. The fruits float, which helps in dispersal.

Uses of Potamogetonaceae 

The Potamogetonaceae family is a cosmopolitan aquatic group of plants that are critical in aquatic environments where they provide food and habitat for aquatic animals, birds, and more. They are a particularly important food source for ducks in North America. Some species are also grown in aquariums.

Morphology of Potamogetonaceae in North America

Some Species of Potamogetonaceae Found in North America

Potamogeton natans—Broad-Leaved Pondweed

This herbaceous aquatic perennial grows in freshwater and has slender to robust stems that are usually simple but can sometimes be branched. Submerged leaves are long and linear, while floating leaves are egg-shaped to elliptic with conspicuous long grass-like stipules. This species has a circumboreal distribution found throughout the Northern Hemisphere. In the Americas it is found in most of Canada and the USA (excluding the southeastern states) and south to southern Mexico along the Pacific coast.

Scientific Botanical Description of the Potamogetonaceae Family

Habit & Leaf Form of the Potamogetonaceae Family

The Potamogetonaceae are a group of perennial aquatic herbs from creeping, rooted rhizomes with leafy branches but no conspicuous aggregations of leaves. Or rarely annuals in the Zannichellieae. They live mostly in fresh water (as opposed to the halophyte Ruppia, which has been suggested should be included in this family), but they can also occasionally be found in ± saline water. Stem growth may be conspicuously sympodial or not.

Leaves may be submerged or submerged and floating and may even be heterophyllous with clearly distinct submerged and floating leaves. Leaves are simple with entire margins and are linear, oblong, or ovate in shape. They are herbaceous or membranous, small to medium in size, and are usually arranged alternately distichous but occasionally may be opposite or in whorls of 3 (especially in Groenlandia). They may be pseudo-petiolate, subsessile, or sessile and are sheathing with usually tubular sheaths with free margins. Venation is one or palmately to parallel-veined, with or without cross-venules.

Leaves are often stipulate or appear so, with some debate over whether ligules are stipules with the sheaths being either free and stipule-like or fused to the leaf base for most of their length. Axillary scales are present in the form of paired intravaginal squamulae. There are no stomata, and the mesophyll has no crystals.

Flowers of the Potamogetonaceae Family

Plants are hermaphrodites with anemophilous or ornithophilous pollination, except in Zannichellieae, where they may be monoecious or rarely dioecious. Flowers are usually in emergent, scapiflorous, spatheate, spicate, or capitate inflorescences, or occasionally with flowers in pairs.

Flowers are small, regular, ebracteate, 4-merous, and tricyclic. The perigone tube is absent. Hypogynous disk absent. Perianth of 4 tepals or absent (if the perianth members are interpreted as staminal appendages); free; members rounded, shortly clawed, valvate, and 1-whorled.

Androecium of the Potamogetonaceae Family

The Potamogetonaceae have 4 androecial members adnate to the claws of the perianth if interpreted as such. They are all equal, free of one another, and 2- or 1-whorled. All members are exclusively fertile stamens, oppositiperianth (when interpreted as such), filantherous, and with sessile anthers or with only sessile anthers (depending on interpretation). Anthers dehisce via longitudinal slits, are extrorse, and may be appendaged (if the tepals are interpreted as outgrowths from the connective) or unappendaged.

Gynoecium of the Potamogetonaceae Family

The gynoecium is apocarpous, superior, and 4(3-8) carpelled. Carpels are usually isomerous with the perianth (or stamens). The carpels are non-stylate or stylate, apically stigmatic, and 1-ovuled. Placentation is marginal to basal (basal-ventral). Stigmas are the dry type, non-papillate, and Group II type. Ovules are pendulous, non-arillate, orthotropous, bitegmic, and crassinucellate.  

Fruit of the Potamogetonaceae Family

Fruits are fleshy or non-fleshy aggregates. The fruiting carpel is indehiscent, nucular, drupaceous, achene, or baccate (Groenlandia). Dispersal usually occurs by the floating of the heads of fruits. The fruits are 1-seeded; the seeds are non-endospermic and contain starch.

Taxonomy of Potamogetonaceae

The Potamogetonaceae family has about 111 species in 4(5) genera of the Alismatales order, a basal monocot. There has been a high degree of hybridization in the family, with chromosome duplication in some.

The very distinctive Zannichellia is weakly embedded in the Potamogetonaceae, but it is sister to Groenlandia, which is sister to the rest of the family, so it is included here.

Genera of the Potamogetonaceae Family:

Althenia (10), Groenlandia (1), Potamogeton (184 when inc. Stuckenia), Pseudalthenia (1 sometimes considered Zannichellia), and Zannichellia (4).  

Key Differences From Similar Families

The Potamogetonaceae are frequently confused with the aquatic family Ruppiaceae, or ditch-grass family. Ruppia is frequently mistaken for narrow-leaved species of Potamogeton because of its similar thread-like leaves and aquatic habitat. However, the Potamogetonaceae are primarily freshwater species as opposed to mostly appearing in variously saline environments with Ruppiaceae. Also, Potamogetonaceae have distinctive stipules that help identify them.

They could also be confused with other aquatic plants, but again, examination of the stipules, environments, and the fruits can separate them fairly easily. Within the Potamogetonaceae, fruits are often the most important features in separating species, so always try to examine the fruits when looking to the genus and species level.

Distribution of Potamogetonaceae

The family has a nearly cosmopolitan distribution, found all over the world except in extreme deserts and extreme cold. In the Americas it is found throughout Canada, the USA, Mexico, Central America, and South America. 

Distribution of Potamogetonaceae in the Americas

Canadian Genera Include:

Potamogeton 45 spp. native everywhere in Canada, including the Arctic (and GreenlandL); Stuckenia (~Potamogeton) 4 spp. native everywhere in Canada, inc. the Arctic (and Greenland); Zannichellia 1 sp., is native almost everywhere in Canada, including the Arctic, but excluding NL.

USA Genera Include:

Potamogeton 53 spp. native and intro to all of the USA, inc. HI, and native to AK; Stuckenia 4 spp. native to all of the USA, inc. AK, and intro in HI; Zannichellia 1 sp. native to almost all of the USA, inc. AK, but exc. SC.

Mexico Genera Include:

Potamogeton 4-10 spp. throughout Mexico; Stuckenia 1 sp. native to BCS, Dgo, Mex, SLP, Son; Zannichellia 1 sp. in Mex.

Neotropical Genera Include:

Potamogeton 17 spp. throughout the neotropics; Stuckenia 3-4 spp in the neotropics, sub-cosmopolitan; Zannichellia 2 spp. cosmopolitan native in the neotropics.

Patagonia Genera Include:

Potamogeton 2 spp. in most of the region, inc. Falkland Islands, but exc. Tierra Del Fuego and Aysen, Chile; Zannichellia 1 sp. native in Santa Cruz, Argentina.

Additional Information and References

• Visit Lyrae’s Dictionary of Botanical Terms to learn the terminology of botanists. Note that if you hover over most of the words in the articles, you can also get definitions from them there.
• Willis, Lyrae (Unpublished). Plant Families of North America. This is where all of the family descriptions come from. Below should be most of my references for this, along with my own personal observations throughout North America.
• Canadensys: Acadia University, Université de Montréal Biodiversity Centre, University of Toronto Mississauga, University of British Columbia. http://data.canadensys.net/explorer (accessed 2020 – current)
• FNA (1993+). Flora of North America. https://floranorthamerica.org/Main_Page. Accessed 2022-current.
• GBIF.org (2020+), GBIF Home Page. Available from: https://www.gbif.org
• iNaturalist.org (2020+). https://www.inaturalist.org/. Accessed 2020-current.
• Naturalista: CONABIO http://www.naturalista.mx (Accessed 2020–current).
• Neotropikey: Milliken, W., Klitgård, B., & Baracat, A. eds. (2009+). Neotropikey: Interactive key and information resources for flowering plants of the Neotropics. www.kew.org/neotropikey.com (accessed 2020 – current).
• Patagonia Wildflowers: Wildflower Identification Site. https://patagoniawildflowers.org/ Accessed throughout the fall of 2020.
• POWO (2019+). Plants of the World Online. Facilitated by the Royal Botanic Gardens, Kew. Published on the Internet: http://www.plantsoftheworldonline.org/
• Stevens, P. F. (2001+). Angiosperm Phylogeny Website. Version 14, July 2017 [more or less continuously updated since]. http://www.mobot.org/MOBOT/research/APweb/
• USDA, NRCS. 2020. The PLANTS Database (http://plants.usda.gov, 2 June 2020). National Plant Data Team, Greensboro, NC, USA; Accessed 2020-present.
• Watson, L., and Dallwitz, M.J. (1992+). The Families of Flowering Plants: descriptions, illustrations, identification, and information retrieval. Version: 2nd May 2020. delta-intkey.com. Accessed spring through fall of 2020.
• WFO (2022): World Flora Online. Published on the Internet: http://www.worldfloraonline.org. Accessed Spring 2022 – current

My Current Plant Family Education Fundraiser

I am currently seeking funding to expand my website and SEO capabilities as I keep adding new families, and I am also looking to invest in a new macro lens, as I will soon be adding floral dissections to the families as they become available to me. You can donate to help support native plant education using the GoFundMe link, also at the bottom of the page.

Copyright Information

The information and the photos on this site are free to use for educational purposes, with proper attribution. For other uses, please contact me first.

You can cite this site as Willis, Lyrae (2020+). Lyrae’s Nature Blog – Plant Families of North America. https://lyraenatureblog.com/