Belongs within: Potamogetonales.
The Potamogetonaceae are a cosmopolitan group of aquatic herbs, often bearing a combination of narrow submerged and broader floating leaves. They first appear in the fossil record in the Late Cretaceous where they are represented by the leaf taxon Potamogetophyllum vernonense (Collinson et al. 1993). Members include the cosmopolitan curled pondweed Potamogeton crispus, in which leaves are entirely submerged and have more or less crimped margins (Healy & Edgar 1980).
Characters (Healy & Edgar 1980): Aquatic perennial herbs of brackish or fresh water. Leaves simple, usually alternate, often dimorphic, submersed ones narrower and more delicate than floating ones; in axil, a delicate membranous stipule, either free or adnate below. Inflorescence a many-flowered spike; peduncle axillary with 0, 1 or 2 bracts at base. Flowers small, green, bisexual, actinomorphic, without bracteoles, segments 4, free, valvate, concave. Stamens 4, on claw of segments; anthers 2-celled, apparently sessile, extrorse. Carpels 4, sessile, free, superior; stigma sessile or nearly so; ovule solitary, strongly curved. Achenes drupe-like when fresh; endocarp stony, splitting by separation of vertically-oriented operculum on outer face.
<==Potamogetonaceae [Potamogetonineae]
|--Diplanthera wrightiiYY22, S00
|--AltheniaYY22
|--GroenlandiaHE80
|--Potamogetophyllum vernonense Fontaine 1905CBH93
`--Potamogeton Linnaeus 1753ME70
| i. s.: P. acutifoliusB78
| P. alpinusH93
| |--P. a. ssp. alpinusH93
| `--P. a. ssp. tenuifoliusH93
| P. amplifoliusB97
| P. capillaceusV72
| P. confervoidesV72
| P. crispus Linnaeus 1753HE80
| P. diversifoliusH93
| P. drummondiiGK00
| P. epihydrusH93
| | i. s.: P. e. var. ramosusV72
| |--P. e. ssp. epihydrusH93
| `--P. e. ssp. nuttalliiH93
| P. fluitansC55
| P. foliosusH93
| |--P. f. var. foliosusH93
| |--P. f. var. fibrillosusH93
| `--P. f. var. macellusV72
| P. friesiiV72
| P. gramineusCS77
| P. hilliiV72
| P. hybridusB78
| P. illinoensisH93
| P. indicusM72
| P. javanicusB78
| P. lateralisV72
| P. latifoliusH93
| P. × longiligulatus [P. strictfolius × P. zosteriformis]V72
| P. lucensC55
| P. miduhikimoW17
| P. mucronatusS00
| P. natansDS04
| P. nodosusPP07
| P. oakesianusV72
| P. obtusifolius [incl. P. compressus]B78
| P. octandrusLK14
| P. perfoliatusC55
| P. polygonifolius Pourr. 1788C06
| P. praelongusH93
| P. pulcherV72
| P. pusillus [incl. P. panormitanus]V72
| |--P. p. var. pusillusH93
| |--P. ‘berchtoldii’ var. lacunatusV72
| |--P. ‘berchtoldii’ var. polyphyllusV72
| `--P. p. var. tenuissimus [incl. P. berchtoldii]H93
| P. richardsonii [=P. perfoliatus var. richardsonii]V72
| P. robbinsiiH93
| P. spirillusV72
| P. strictifoliusV72
| P. tenuicaulisB78
| P. tricarinatusLK14
| P. vaseyiV72
| P. zosterifoliusV72
| P. zosteriformisH93
|--P. subg. PotamogetonME70
| |--P. cheesemanii Bennett 1883ME70 (see below for synonymy)
| |--P. ochreatus Raoul 1844ME70
| `--P. suboblongus Hagström 1916ME70
`--P. subg. ColeogetonKG01
|--P. × bottnicus [P. pectinatus × P. vaginatus]KG01
|--P. filiformisKG01
| |--P. f. var. filiformisV72
| |--P. f. var. borealisV72
| `--P. f. var. macouniiV72
|--P. pectinatus Linnaeus 1753ME70
|--P. × suecicus [P. pectinatus × P. filiformis]KG01
`--P. vaginatusKG01
Potamogeton cheesemanii Bennett 1883ME70 [incl. P. natans var. australis Kirk ex Bennett 1887C06, P. cheesemanii f. corymboides Hagström 1916ME70, P. cheesemanii f. frondosus Hagström 1916ME70, P. membranaceus Hagström 1916ME70, P. porrigens Hagström 1916ME70]
*Type species of generic name indicated
References
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[CS77] Cramp, S., & K. E. L. Simmons (eds) 1977. Handbook of the Birds of Europe, the Middle East and North Africa: The Birds of the Western Palaearctic vol. 1. Ostrich to Ducks. Oxford University Press: Oxford.
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[HE80] Healy, A. J., & E. Edgar. 1980. Flora of New Zealand vol. 3. Adventive cyperaceous, petalous and spathaceous monocotyledons. P. D. Hasselberg, Government Printer: Wellington (New Zealand).
[H93] Hickman, J. C. (ed.) 1993. The Jepson Manual: Higher Plants of California. University of California Press: Berkeley (California).
[KG01] King, R. A., R. J. Gornall, C. D. Preston & J. M. Croft. 2001. Molecular confirmation of Potamogeton × bottnicus (P. pectinatus × P. vaginatus, Potamogetonaceae) in Britain. Botanical Journal of the Linnean Society 135 (1): 67–70.
[LK14] Lyons, M. N., G. J. Keighery, L. A. Gibson & T. Handasyde. 2014. Flora and vegetation communities of selected islands off the Kimberley coast of Western Australia. Records of the Western Australian Museum Supplement 81: 205–244.
[M72] Mitra, S. N. 1972. Observations on the vegetation of the Upper Damodar catchment area. Journal of the Bombay Natural History Society 69 (1): 17–25.
[PP07] Pandey, R. P., & P. M. Padhye. 2007. Studies on phytodiversity of Arid Machia Safari Park-Kailana in Jodhpur (Rajasthan). Bulletin of the Botanical Survey of India 49: 15–78.
[S00] Siddiqi, M. R. 2000. Tylenchida: Parasites of plants and insects 2nd ed. CABI Publishing: Wallingford (UK).
[V72] Voss, E. G. 1972. Michigan Flora. Part I. Gymnosperms and Monocots. Cranbrook Institute of Science and University of Michigan Herbarium.
[W17] Weber, C. A. 1917. Die Pflanzenwelt des Rabutzer Beckentons und ihre Entwicklung unter Bezugnahme auf Klima und geologische Vorgänge. Botanische Jahrbücher für Systematik, Pflanzengeschichte und Pflanzengeographie 54 (Beiblatt 120): 3–50.
[YY22] Yampolsky, C., & H. Yampolsky. 1922. Distribution of sex forms in the phanerogamic flora. Bibliotheca Genetica 3: 1–62.