''Potamogeton obtusifolius'', known as blunt-leaved pondweed, is an

aquatic plant Aquatic plants, also referred to as hydrophytes, are vascular plants and Non-vascular plant, non-vascular plants that have adapted to live in aquatic ecosystem, aquatic environments (marine ecosystem, saltwater or freshwater ecosystem, freshwater ...

in the

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

''Potamogeton''. It grows mainly in mesotrophic to

eutrophic Eutrophication is a general term describing a process in which nutrients accumulate in a body of water, resulting in an increased growth of organisms that may deplete the oxygen in the water; ie. the process of too many plants growing on the s ...

lakes, ponds and ditches, rarely in

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

water. It occurs primarily in Central Europe, the British Isles, Fennoscandia and eastern North America.

Description

Blunt-leaved pondweed grows annually from turions and seed, producing branching plants with slender, flattened stems that have well-developed nodal glands (these appear as two raised bumps on the stem where the leaf attaches). The submerged leaves are long, rather grass-like,

sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...

, translucent leaves that are 48–85 (rarely up to 100) mm long and 1.5–3.55 mm wide and pale green, often with a very marked reddish or brownish tinge and a pink tinge along the midrib. There are 1–2 lateral veins either side of the midrib. As the name suggests, the leaf tips are rather blunt, though close inspection usually reveals a narrow point at the tip. The

stipule In botany, a stipule is an outgrowth typically borne on both sides (sometimes on just one side) of the base of a leafstalk (the petiole (botany), petiole). They are primarily found among dicots and rare among monocots. Stipules are considered part ...

s are open. There are no rhizomes or floating leaves. Abundant turions are produced along the stem, especially in autumn as the plant disintegrates. The flower spikes of blunt-leaved pondweed are rather short and dense, 4–9 mm long with 6–8 flowers in each. Fruits, which are approximately 3 × 2 mm, are freely produced. Blunt-leaved pondweed could be confused with other fine-leaved pondweeds within its range, especially ''

Potamogeton berchtoldii ''Potamogeton berchtoldii'', common name small pondweed, is an aquatic plant. Description Small pondweed is a fine-leaved pondweeds with a bushy habit. It lacks a perennial rhizome and the plants die back in winter into a large number of resting ...

'' and ''P. friesii'', but potentially also '' P. pusillus''. The combination of open stipules, rounded tips to the leaves, dense flower spikes and a tendency to produce a mass of bushy growth at the surface all help to distinguish this plant, but use of a botanical key or flora is recommended. ''Potamogeton obtusifolius'' is diploid, with 2n=26. According to a key monograph on the genus, no hybrids of ''Potamogeton obtusifolius'' have been confirmed. However, ''P''. × ''saxonicus'' Hagstr. has been suggested to be the hybrid with ''P. pusillus''.

Taxonomy

Blunt-leaved pondweed was first described in 1823 by

Franz Carl Mertens Franz Carl Mertens (3 April 1764 – 19 June 1831) was a German botanist who was a native of Bielefeld. He specialized in the field of phycology. Mertens studied theology and languages at the University of Halle, and after graduation taught ...

and

Wilhelm Daniel Joseph Koch Wilhelm Daniel Joseph Koch (5 March 1771 – 14 November 1849) was a German physician and botanist from Kusel, which at various points in his life was under the Holy Roman Empire, part of France and then part of the Kingdom of Bavaria. Education ...

. The specific name ''obtusifolius'' means 'blunt-leaved'. It is related to other fine-leaved pondweeds, such as ''P. friesii'' and ''P. pusillus''. Wang et al. have suggested based on DNA analysis that ''P. obtusifolius'' may have arisen through hybridisation between '' P. compressus'' and ''P. pusillus''.

Distribution

''Potamogeton obtusifolius'' has a wide global distribution, occurring in North America (Canada, northern US), Europe (Scandinavia, Central Europe, N Balkans, Great Britain, Ireland, France, N Spain), Asia (NE China (

Heilongjiang Province Heilongjiang is a province in northeast China. It is the northernmost and easternmost province of the country and contains China's northernmost point (in Mohe City along the Amur) and easternmost point (at the confluence of the Amur and Ussu ...

), Russia, Japan, Kazakhstan, Kyrgyzstan, Mongolia, Myanmar, Caucasus, Iran).

Ecology and conservation

In Britain, ''P. obtusifolius'' occurs in a range of standing water habitats including ponds, ditches, canals and shallow lakes, favouring circumneutral or slightly acidic waters. It is strictly a lowland plant and rarely observed in running water, except where current speeds are very slow. Although widely distributed it has a patchy distribution and is not usually abundant at any individual site. Like other fine-leaved pondweeds, ''P. obtusifolius'' probably benefits from a certain amount of disturbance to suppress competing vegetation. It seems to favour smaller water bodies and apparently tolerates poor water quality, including turbid water, reasonably well. In spite of this, blunt-leaved pondweed does not usually proliferate in eutrophic lakes. It is possible that this species is rather sensitive to wind action. In cultivation, ''P. obtusifolius'' leaves were eaten by three different species of

chironomid Chironomidae , commonly known as non-biting midges or chironomids , are a family of Nematoceran flies with a global distribution. They are closely related to the families Ceratopogonidae, Simuliidae, and Thaumaleidae. Although many chironomid s ...

(non-biting midge) larvae. Globally and in various national Red Lists, blunt-leaved pondweed is considered Least Concern. However, blunt-leaved pondweed has suffered local declines and is Critically Endangered in Switzerland, Vulnerable in Germany, Very Rare in Luxemburg, listed as Endangered in New Jersey and Pennsylvania, and Sensitive in Washington. It is considered to have declined in Britain, but is still widespread, and listed as Least Concern.

Cultivation

Blunt-leaved pondweed is not presently in cultivation. Although its wide ecological tolerance suggests it may not be difficult to grow, it would probably require a deeper substrate than is usual in most ponds. It can also be grown in aquaria by anchoring the turions in sand or mud. It is also likely to compete poorly with other pond plants.

References

External links

* {{Taxonbar, from=Q160722 obtusifolius Taxa named by Franz Carl Mertens Taxa named by Wilhelm Daniel Joseph Koch