80–100, see text
Potamogeton is a genus of aquatic, mostly freshwater, plants of the family Potamogetonaceae. Most are known by the common name pondweed, although many unrelated plants may be called pondweed, such as Canadian pondweed (Elodea canadensis). The genus name means "river neighbor", originating from the Greek potamos (river) and geiton (neighbor).
Potamogeton species range from large (stems of 6 m or more) to very small (less than 10 cm). Height is strongly influenced by environmental conditions, particularly water depth. All species are technically perennial, but some species disintegrate in autumn to a large number of asexually produced resting buds called turions, which serve both as a means of overwintering and dispersal. Turions may be borne on the rhizome, on the stem, or on stolons from the rhizome. Most species, however, persist by perennial creeping rhizomes. The leaves are alternate, which contrasts with the closely related genus Groenlandia, where the leaves are opposite or whorled.
In many species, all the leaves are submerged, and in these cases, they are typically thin and translucent. Some species, especially in ponds and very slow-moving waters, have floating leaves which tend to be opaque with a leathery texture.
All Potamogeton have a delicate membranous sheathing scale, the stipule, at the leaf axil. This may be wholly attached, partly attached, or free of the leaf, and it may have inrolled margins or appear as a tube. The morphology of the stipule is an important character for species identification. The flowers, which are often overlooked, are greenish-brown and are composed of four rounded segments borne in a spike. The fruits are spheroidal and green to brown, usually 1–3 mm in diameter, with a noticeable 'beak'.
Most fine-leaved pondweeds are diploid, with 2n = 26 (such as P. pusillus or P. trichoides) or less commonly 28 (P. compressus, P. acutifolius). Broad-leaved taxa are mainly tetraploid, with 2n = 52 (e.g. P. alpinus, P. praelongus), but a few species are diploid (e.g. P. coloratus or octaploid (2n = 104)(e.g. P. illinoensis).
Potamogeton species are found throughout the world in standing or running water. In a detailed review of the genus, Wiegleb and Kaplan recognised 69 species, but the variability of many species means that there is disagreement regarding the exact number of species. Currently, the number of accepted names is 94. Hybridisation provides an added complexity to the taxonomy.
The genus has been split into several sections. Section Potamogeton contains the larger broad-leaved species such as P. natans, P. perfoliatus and P. alpinus. Section Graminifolii consists of fine-leaved species such as P. rutilus, P. compressus and P. berchtoldii. Series Batrachoseris contains only one species, Potamogeton crispus. Subgenus Coleogeton, containing P. pectinatus, P. filiformis and P. vaginatus, is now considered to belong to a separate genus, Stuckenia. These general divisions have been supported by molecular analysis, except that P. crispus clusters with broad-leaved species in section Potamogeton.
Potamogeton species are found worldwide in many aquatic ecosystems. However, the greatest diversity of species occurs in the northern hemisphere, especially in North America, which is thought to be where the genus originated. Molecular evidence suggests that several independent colonizations of the southern hemisphere have occurred.
Potamogeton species hybridise freely. At least 27 hybrids have been observed in the British Isles alone, and more than 50 worldwide, of which 36 have been confirmed using genetic techniques. The majority of these are sterile, but many are long-lived and may occur in the absence of one or even both parents. Most hybrids have been described between broad-leaved species, but this probably reflects the relative scarcity of characters among fine-leaved taxa, so that hybrids are much more difficult to identify. Use of genetic markers suggests that hybrid taxa are also reasonably frequent among fine-leaved species. At least one species, P. obtusifolius, is thought to have arisen via hybridisation.
Several species of European pondweeds, including P. natans, P. lucens and P. crispus, were included in Linnaeus's Species Plantarum in 1753. Much of the European Potamogeton flora was subsequently named during the late 18th and early 19th century. As botanists ventured further afield, pondweeds began to be collected and named from other parts of the world. The North America flora was largely named by the start of the 20th century. Alfred Fryer became interested in Potamogeton in the 1880s, and was a recognised authority on the genus. The first parts of his work The Potamogetons (Pond Weeds) of the British Isles were published in 1898. His death intervened, and the work was completed by Arthur Bennett (1843-1929), who named a large number of specimens sent to him from around the world. Robert Morgan (1863-1900) illustrated Fryer's contribution to the monograph, his colour plates drawing praise from later critics.
New species continue to be described from less well-studied areas such as Asia and Africa, and it is possible that molecular analysis may reveal hitherto unknown cryptic species.
List of Potamogeton species
- P. acutifolius Link ex Roem. & Schult. 1818
- P. alpinus Balb. 1804
- P. amplifolius Tuck. 1848
- P. antaicus Hagstr. 1916
- P. australiensis A.Benn. 1910
- P. berchtoldii Fieber 1838
- P. bicupulatus Fernald 1932
- P. biformis Hagstr. 1916
- P. brasiliensis A.Benn. 1910
- P. chamissoi A.Benn. 1904
- P. cheesemanii A.Benn. 1883
- P. chongyangensis W.X.Wang 1984
- P. coloratus Hornem. 1813
- P. compressus L. 1753
- P. confervoides Rchb. 1845
- P. crispus L. 1753
- P. cristatus Regel & Maack, 1861
- P. delavayi A.Benn. 1892
- P. distinctus A. Benn. 1904
- P. diversifolius Raf. 1811
- P. drummondii Benth. 1878
- P. epihydrus Raf. 1811
- P. ferrugineus Hagstr. 1916
- P. floridanus Small 1903
- P. foliosus Raf. 1811
- P. fontigenus Y.H.Guo, X.Z.Sun & H.Q.Wang 1985
- P. friesii Rupr. 1845
- P. fryeri A.Benn. 1907
- P. gayi A.Benn. 1892
- P. gramineus L. 1753
- P. heterocaulis Z.S.Diao 1994
- P. hillii Morong 1881
- P. hoggarensis Dandy 1937
- P. illinoensis Morong 1880
- P. intortusifolius J.B.He, L.Y.Zhou & H.Q.Wang 1988
- P. iriomotensis Masam. 1934
- P. juzepczukii P.I.Dorof. & Tzvelev 1983
- P. kashiensis Z.S.Diao 1995
- P. lacunatifolius Papch. 2001
- P. linguatus Hagstr. 1901
- P. lucens L. 1753
- P. maackianus A.Benn. 1904
- P. mandschuriensis (A.Benn.) A.Benn. 1924
- P. marianensis Cham. & Schltdl. 1827
- P. montevidensis A.Benn. 1892
- P. nanus Y.D.Chen 1987
- P. natans L. 1753
- P. nodosus Poir. 1816
- P. nomotoensis Kadono & T.Nog. 1991
- P. oakesianus J.W.Robbins 1867
- P. obtusifolius Mert. & W.D.J.Koch 1823
- P. ochreatus Raoul 1844
- P. octandrus Poir. 1816
- P. ogdenii Hellq. & R.L.Hilton 1983
- P. oxyphyllus Miq. 1867
- P. papuanicus G.Wiegleb 1993
- P. paramoanus R.R.Haynes & Holm-Niels. 1982
- P. parmatus Hagstr. 1908
- P. perfoliatus L. 1753
- P. polygonifolius Pourr. 1788
- P. polygonus Cham. & Schltdl. 1827
- P. praelongus Wulfen 1805
- P. pulcher Tuck. 1843
- P. punense A.Galán 1988
- P. pusillus L. 1753
- P. quinquenervius Hagstr. 1916
- P. reniacoensis Sparre 1956
- P. richardii Solms 1867
- P. richardsonii (A.Benn.) Rydb. 1905
- P. robbinsii Oakes 1841
- P. rutilus Wolfg. 1827
- P. sarmaticus Mäemets 1978 publ. 1979
- P. schweinfurthii A.Benn. 1901
- P. sclerocarpus K.Schum. 1894
- P. sibiricus A.Benn. 1890
- P. skvortsovii Klinkova 1993
- P. solomonensis G.Wiegleb 1993
- P. spathuliformis (J.W.Robbins) Morong 1893
- P. spirilliformis Hagstr. 1916
- P. spirillus Tuck. 1848
- P. stenostachys K.Schum. 1894
- P. strictifolius A.Benn. 1902
- P. subnitens Hagstr. 1916
- P. suboblongus Hagstr. 1916
- P. sumatranus Miq. 1861
- P. tennesseensis Fernald 1936
- P. tepperi A.Benn. 1887
- P. tricarinatus F.Muell. & A.Benn. 1892
- P. trichoides Cham. & Schltdl. 1827
- P. tubulatus Hagstr. 1922
- P. ulei K.Schum. 1894
- P. uruguayensis A.Benn. & Graebn.
- P. vaseyi J.W.Robbins 1867
- P. wrightii Morong 1886
List of Potamogeton hybrids
- P. × anguillanus Koidz.
- P. × angustifolius J.Presl
- P. × apertus Miki
- P. × argutulus Hagstr.
- P. × attenuatus Hagstr.
- P. × babingtonii A.Benn.
- P. × billupsii Fryer
- P. × cadburyae Dandy & G.Taylor
- P. × cognatus Asch. & Graebn.
- P. × cooperi (Fryer) Fryer
- P. × faurei (A.Benn.) Miki
- P. × fluitans Roth
- P. × franconicus G.Fisch.
- P. × gessnacensis G.Fisch.
- P. × griffithii A.Benn.
- P. × grovesii Dandy & G.Taylor
- P. × haynesii Hellq. & G.E.Crow
- P. × inbaensis Kadono
- P. × kamogawaensis Miki
- P. × kyushuensis Kadono & Wiegleb
- P. × lanceolatifolius (Tiselius) C.D.Preston
- P. × lanceolatus Sm.
- P. × leptocephalus Koidz.
- P. × lintonii Fryer
- P. × malainoides Miki
- P. × mariensis Papch.
- P. × mysticus Morong
- P. × nericius Hagstr.
- P. × nerviger Wolfg.
- P. × nitens Weber
- P. × olivaceus Baagøe ex G.Fisch.
- P. × orientalis Hagstr.
- P. × philippinensis A.Benn.
- P. × prussicus Hagstr.
- P. × pseudofriesii Dandy & G.Taylor
- P. × rectifolius A.Benn.
- P. × salicifolius Wolfg.
- P. × schreberi G.Fisch.
- P. × scoliophyllus Hagstr.
- P. × sparganiifolius Laest. ex Fr.
- P. × spathulatus Schrad. ex W.D.J.Koch & Ziz
- P. × subsessilis Hagstr.
- P. × sudermanicus Hagstr.
- P. × undulatus Wolfg.
- P. × vaginans (Bojer ex A.Benn.) Hagstr.
- P. × varians Morong
- P. × variifolius Thore
- P. × vepsicus A.A.Bobrov & Chemeris
- List source :
Propagation of pondweeds occurs both vegetatively and by seed, though studies suggest that in some species and / or situations propagation by seed is rare. The fruits may be produced in large quantities from midsumer onwards, and are ingested by waterfowl. Germination experiments have shown that the seeds are viable after passing through the digestive tracts of birds and this mechanism is probably the only natural mechanism for long-distance dispersal and between isolated water bodies. Vegetative propagation occurs by a variety of mechanisms including turions, and via growth and fragmentation of rhizomes and shoots. Vegetative reproduction is evidently an effective means of ensuring local persistence, as sterile hybrids have been recorded at some sites for over 100 years.
Although they occur in a range of environments, most species prefer standing or slow-flowing waters with some calcium and fairly low nutrient levels. In general the fine-leaved species are more tolerant of human impacts such as eutrophication. They are important as food and habitat for animals including insect larvae, water snails, ducks and other waterfowl, and aquatic mammals such as beavers.
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- "Potamogeton". The Plant List; Version 1.1 (published on the internet). Royal Botanic Gardens, Kew and Missouri Botanical Garden. 2010. Retrieved November 16, 2014.
- Preston C.D. (1995). Pondweeds of Great Britain and Ireland. BSBI Handbook No. 8. Botanical Society of the British Isles, London.
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- Ito, Y., and Nr. Tanaka (2013) Additional Potamogeton hybrids from China: Evidence from a comparison of plastid trnT–trnF and nuclear ITS phylogenies. APG: Acta Phytotaxonomica et Geobotanica 64 (1): 1–14
- Zalewska-Galosz J., Ronikier M. 2010. Are linear-leaved Potamogeton hybrids really so rare? Molecular evidence for multiple hybridizations between P. acutifolius and P.compressus in Central Europe. Nordic Journal of Botany, 28, 257-261.
- Wang Q.D., Zhang T., Wang J.B. 2007. Phylogenetic relationships and hybrid origin of Potamogeton species (Potamogetonaceae) distributed in China: insights from the nuclear ribosomal internal transcribed spacer sequence (ITS). Plant Systematics and Evolution, 267, 65-78.
- Preston C.D. 1988. The Potamogeton L. species and hybrids described by Alfred Fryer. Watsonia, 17 23-35.
- http://www.watsonia.org.uk/Wats16p217.pdf[dead link]
- "Fryer, Alfred (1826 – 1912)".
- Brux H., Todeskino D, Wiegleb G. 1987. Growth and reproduction of Potamogeton alpinus Balbis growing in disturbed habitats. Archiv für Hydrobiologie, 27, 115-127.
- UK Water Framework Directive Technical Advisory Group (UKTAG). 2014. UKTAG River Assessment Method: Macrophytes and Phytobenthos: Macrophytes (River LEAFPACS2). ISBN 978-1-906934-44-6. Available online at River Leafpacs
- UK Water Framework Directive Technical Advisory Group (UKTAG). 2014. UKTAG Lake Assessment Method: Macrophytes and Phytobenthos: Macrophytes (Lake LEAFPACS2). ISBN 978-1-906934-45-3. Available online at Lakes Leafpacs
- "Pondweeds: Potamogeton species". Center for Aquatic and Invasive Plants; University of Florida / IFAS. 2011. Retrieved January 6, 2012.
- "Curly leaf pondweed: Potamogeton crispus L.". Center for Invasive Species and Ecosystem Health. May 4, 2010. Retrieved January 6, 2012.