Potamogeton praelongus

Potamogeton praelongus, commonly known as whitestem pondweed in North America[2] and Long-stalked Pondweed in Britain,[3] is a large, perennial aquatic plant in the family Potamogetonaceae. It is widely distributed in lakes and rivers in the northern hemisphere, but is sensitive to poor water quality.

Potamogeton praelongus
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Order: Alismatales
Family: Potamogetonaceae
Genus: Potamogeton
Species:
P. praelongus
Binomial name
Potamogeton praelongus
Synonyms[1]

Potamogeton acuminatus Wahlenb. Potamogeton flexuosus Wredow Potamogeton flexuosus Schleich. Spirillus praelongus (Wulfen.) Nieuwl.

Description

Long-stalked pondweed has tall stems to 3 m growing from stout, rusty-spotted perennial rhizomes.[4] The stems often change direction between each node, giving a characteristic zig-zagging pattern. The transparent pale to deep green leaves[5][6] are typically between 60 and 150 mm long but occasionally reach 250 mm[7] and are 14–40 mm wide.[6] The stipules are persistent, open, whitish and translucent, with prominent veins when dry.[6] Floating leaves and turions are absent.[7] The inflorescences are produced quite early for a pondweed, in May–June, and have 15-20 inconspicuous greenish flowers and held on robust peduncles 80–200 mm long.[6] The fruits are large for a pondweed, 4.5-5.5 x 2.5-3.6 mm.[6]

Long-stalked pondweed Potamogeton praelongus growing in deep, very clear water in a lake in North Wales.

Hybrids with several other species, P. alpinus (P. × griffithii A. Benn.), P. crispus (P. × undulatus Wolgf.), P. lucens (P. × jutlandicus Zalewska-Gał.), P. natans (P. × vepsicus A.A. Bobrov & Chemeris) and P. perfoliatus (P. × cognatus Asch. & Graebn.) have been described, but all are rare.[6][8][9] Chromosome counts[10] show that, like most other broad-leaved pondweeds, P. praelongus is tetraploid, with 2n=52 chromosomes.

Long-stalked pondweed is relatively easy to identify. It could be confused with narrow-leaved forms of Potamogeton perfoliatus, but the persistent stipules, leaves only partially clasping the stem, larger fruits and (usually) zigzag pattern of the stem are distinctive. Hybrids may be more difficult to identify but usually show various features of the other parent.

Taxonomy

Long-stalked pondweed was first described in 1805 by the German taxonomist Franz von Wulfen.[1] The specific epithet means 'very long'. It is not a particularly variable species and consequently there are few synonyms.

Potamogeton praelongus sits within series Potamogeton, which includes other broad-leaved species such as P. alpinus and P. perfoliatus.[6]

Distribution

Potamogeton praelongus has a Holarctic distribution, occurring in northern Europe (Britain,[6] Ireland, Iceland, Scandinavia, Germany, Switzerland, France, Poland, Russia, the Baltic States),[11] Greenland,[12] Asia (Siberia, China, Korea, Japan),[7][11] North America (northern USA, Canada).[5][11] There are outlying populations in the Caucasus, Pyrenees and western USA.[11][13]

Ecological Requirements and Conservation

Ecological Requirements

P. praelongus requires clear, deep water with at least some basic influence,[14] and rarely grows in water less than 1 m deep.[6] In Britain is usually found in lakes with limestone, marl or basalt geology,[6] and it is absent from acidic lakes such as are common in Wales. It also occurs in slow-flowing rivers and disused canals. Long-stalked pondweed tends to be a rather rare plant within its range; for example, in a study of more than 3,500 British lakes, it occurred in only 88, most of which had low-moderate alkalinity and were dominated by isoetids.[14] The seeds require a cold period to encourage germination.[15]

Conservation and threats

Long-stalked pondweed is relatively sensitive to eutrophication and declines or local extinctions of this species have been associated with increased nutrent levels.[16][17][18] In Loch Leven (Scotland), P. praelongus was lost due to eutrophication during the mid 20th century, but has recently reappeared following improvements to water quality.[19]

Globally, P. praelongus is listed as Least Concern.[13] However, it has undergone a marked decline in parts of its range, especially Europe. In the British Red List for Vascular Plants it is listed as Near Threatened[20] due in particular to a marked decline in southern Britain, likely linked to eutrophication;[21] assessments in England[22] and Wales[23] have recently categorised it as Endangered and Critically Endangered respectively. In Spain,[24] Germany[25] and the Czech Republic P. praelongus is Critically Endangered: the Czechs have an active conservation plan in place to propagate it and introduce it to new locations.[26] It is also listed as Endangered in Switzerland,[27] several US states[28] and some French départements,[13] Vulnerable in the Netherlands,[29] and Extinct in Flanders.[30] Long-stalked pondweed is one of the so-called Magnopotamion group of pondweeds. These are a characteristic floristic component of the protected Habitats Directive habitat Type 'Natural eutrophic lakes with Magnopotamion'.[31] However, in Britain at least, P. praelongus is now predominantly found in oligotrophic to mesotrophic waters.

Cultivation

P. praelongus is not in general cultivation, though it is an attractive plant. Unlike many other pondweeds it remains wintergreen. In common with other pondweeds of this group it roots poorly from stem cuttings and is best propagated by division of the rhizomes. Its preference for relatively deep water and intolerance of turbid conditions may make it unsuitable for many garden ponds. If possible it should be grown in water at least 70 cm deep on a sandy, peaty or silty substrate. Good water quality is needed to reduce the risk of turbid water or growth of blanket weed. Seed can be encouraged to germinate by immersing dried seed in water for at least a month, exposing them to a cold period, or by scarifying them.[15]

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References
  1. The Plant List: Potamogeton praelongus. Royal Botanic Gardens, Kew and Missouri Botanic Gardens. Accessed November 18, 2014
  2. "Potamogeton praelongus". Natural Resources Conservation Service PLANTS Database. USDA. Retrieved 13 October 2015.
  3. "BSBI List 2007". Botanical Society of Britain and Ireland. Archived from the original (xls) on 2015-01-25. Retrieved 2014-10-17.
  4. "Ohio DNR: Potamogeton praelongus". Retrieved 2008-06-16.
  5. Haynes R.R., Hellquist C.B. Flora of North America: Potamogetonaceae. Accessed 11 November 2014.
  6. Preston C.D. (1995). Pondweeds of Great Britain and Ireland. BSBI Handbook No. 8. Botanical Society of the British Isles, London.
  7. Guo Y., Haynes R.R., Hellquist C.B., Kaplan Z. 2010. Potamogeton. Flora of China, 23, 108-114.
  8. Zalewska-Gałosz J. 2011. Potamogeton ×jutlandicus, a binominal for the hybrid between P. lucens and P. praelongus (Potamogetonaceae). Nordic Journal of Botany, 29, 473-476.
  9. Zalewska-Gałosz J., Ronikier M. 2012. Molecular evidence for two rare Potamogeton natans hybrids with reassessment of Potamogeton hybrid diversity in Poland. Aquatic Botany, 103, 15-22.
  10. 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.
  11. Naturhistorika riksmuseet (Sweden) Den virtuellen flora: långnate Potamogeton praelongus L., northern hemisphere range map
  12. Bennike O., Anderson J.N. 1998. Potamogeton praelongus in West Greenland. Nordic Journal of Botany, 18, 499-501
  13. Lansdown, R.V. 2014. Potamogeton praelongus. The IUCN Red List of Threatened Species. Version 2014.2. Downloaded on 26 October 2014.
  14. Duigan C., Kovach W., Palmer M. 2006. Vegetation communities of British lakes: a revised classification. Joint Nature Conservation Committee, Peterborough.
  15. Prausová R., Sikorová P., Šafářová L. 2014. Generative reproduction of long stalked pondweed (Potamogeton praelongus Wulfen) in the laboratory. Aquatic Botany (in press)
  16. Morgan N.C. 1970. Changes in the fauna and flora of a nutrient enriched lake. Hydrobiologia, 35, 545-553.
  17. Egertson C.J., Kopaska J.A., Downing J.A. 2004. A Century of Change in Macrophyte Abundance and Composition in Response to Agricultural Eutrophication. Hydrobiologia, 524, 145-156.
  18. Sand-Jensen K, Riis T, Vestergaard O. Larsen S.E. 2000. Macrophyte decline in Danish lakes and streams over the past 100 years. Journal of Ecology, 88, 1030-1040.
  19. Dudley B., Gunn I., Carvalho L., Proctor I., O’Hare M., Murphy K., Milligan A. 2011. Changes in aquatic macrophyte communities in Loch Leven: evidence of recovery from eutrophication? Hydrobiologia, 681, 49-57
  20. 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.
  21. Preston C.D., Pearman D.A., Dines T.D. 2002. New Atlas of the British and Irish Flora: An Atlas of the Vascular Plants of Britain, Ireland, the Isle of Man and the Channel Islands. Oxford University Press, Oxford.
  22. "Stroh P.A., Leach S.J., August T.A., Walker K.J., Pearman D.A., Rumsey F.J., Harrower C.A., Fay M.F., Martin J.P., Pankhurst T., Preston C.D. & Taylor I. 2014. A Vascular Plant Red List for England. Botanical Society of Britain and Ireland, Bristol" (PDF). Archived from the original (PDF) on 2014-11-12. Retrieved 2014-11-11.
  23. "Dines T.D. 2008. A Vascular Plant Red List for Wales. Plantlife International, Salisbury". Archived from the original on 2014-11-12. Retrieved 2014-11-11.
  24. Moreno, J.C., coord. 2008. Lista Roja 2008 de la flora vascular española. Dirección General de Medio Natural y Política Forestal (Ministerio de Medio Ambiente, y Medio Rural y Marino, y Sociedad Española de Biología de la Conservación de Plantas), Madrid, 86 pp.
  25. Bundesamt fur Naturschutz: Potamogeton praelongus (in German)
  26. Prausová R., Janová J., Adamec L. 2011. Rescue of the critically endangered long-stalked pondweed (Potamogeton praelongus) in the Czech Republic. Acta Biologica Slovenica, 54, 43-54.
  27. Moser D.M., Gygax A., Bäumler B., Wyler N., Palese R. 2002. Liste rouge des espèces menacées de Suisse. Fougères et plantes à fleurs. Ed. Office fédéral de l’environnement, des forêts et du paysage, Berne; Centre du Réseau Suisse de Floristique, Chambésy; Conservatoire et Jardin botaniques de la Ville de Genève, Chambésy. Série OFEFP «L’environnement pratique». 118 pp.
  28. United States Department of Agriculture (USDA) Natural Resources Conservation Service: Plants Profile for Potamogeton praelongus. Accessed 25 October 2014.
  29. Sparrius L.B., Odé B., Beringen R. 2014. Basisreport Rode Lijst Vaatplanten 2012 volgens Nederlandse en IUCN-criteria. FLORON Rapport 57. Floron, Nijmegen.
  30. Van Landuyt W., Vanhecke L., Hoste I. 2006. Rode Lijst van de vaatplanten van Vlaanderen en het Brussels Hoofdstedelijk Gewest. In : Van Landuyt W. et al. Atlas van de Flora van Vlaanderen en het Brussels Gewest. INBO en Nationale Plantentuin van België, Brussel. Web version.
  31. "Joint Nature Conservation Committee: 3150 Natural Eutrophic Lakes". Retrieved 2014-10-19.
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