''Elodea canadensis'' (American waterweed or Canadian waterweed or pondweed) is a perennial

aquatic plant Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes. A macrophyte is a plant that ...

, or submergent macrophyte, native to most of

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

.Flora of North America
''Elodea canadensis''
/ref>Plants of British Columbia
''Elodea canadensis''
/ref>Jepson Flora
''Elodea canadensis''
/ref> It has been introduced widely to regions outside its native range and was first recorded from the British Isles in about 1836.

Distribution

The native range of the species lies within North America, but it has been introduced in many parts of the world either intentionally or not. Europe has been particularly affected with the first record dating back as far as 1836. Since then, the species' presence has been confirmed in all continental European countries. Records of the species' presence in Ireland include: County Galway, found at several sites along the Eglinton Canal, County Galway, County Down. and from the Lagan Canal near

Lisburn Lisburn (; ) is a city in Northern Ireland. It is southwest of Belfast city centre, on the River Lagan, which forms the boundary between County Antrim and County Down. First laid out in the 17th century by English and Welsh settlers, with ...

, Northern Ireland.

Description

Young plants initially start with a seedling stem with roots growing in mud at the bottom of the water; further adventitious roots are produced at intervals along the stem, which may hang free in the water or anchor into the bottom. It grows indefinitely at the stem tips, and single specimens may reach lengths of 3 m or more. The

leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...

are bright green, translucent, oblong, 6–17 mm long and 1–4 mm broad, borne in whorls of three (rarely two or four) round the stem. It lives entirely underwater, the only exception being the small white or pale purple flowers which float at the surface and are attached to the plant by delicate stalks.These stalks, or hypanthea, are the lower part of the petals joined to form a floral tube. This floral tube can be up to 30 centimeters (12 inches) in length while only 1/25 inch (one millimeter) in width. for a length to width ratio of 300 fold. However, according to Wilie this ratio can sometimes be as much as ''one thousand fold,'' making this by a wide margin the skinniest of all flowers. It is

dioecious Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproductio ...

, with male and female flowers on different plants. The flowers have three small white petals; male flowers have 4.5–5 mm petals and nine stamens, female flowers have 2–3 mm petals and three fused carpels. The fruit is an ovoid capsule, about 6 mm long containing several seeds that ripen underwater. The seeds are 4–5 mm long, fusiform, glabrous (round), and narrowly cylindrical. It flowers from May to October.Huxley, A., ed. (1992). ''New RHS Dictionary of Gardening''. Macmillan . It grows rapidly in favorable conditions and can choke shallow ponds, canals, and the margins of some slow-flowing rivers. It requires summer water temperatures of 10–25 °C and moderate to bright lighting. It is closely related to ''

Elodea nuttallii ''Elodea nuttallii'' is a species of waterweed known by the common name western waterweed or Nuttall's waterweed. This is a perennial aquatic plant which is native to North America where it grows submersed in lakes, rivers, and other shallow wa ...

'', which generally has narrower leaves under 2 mm broad. It is usually fairly easy to distinguish from its relatives, like the Brazilian '' Egeria densa'' and ''

Hydrilla verticillata ''Hydrilla'' (waterthyme) is a genus of aquatic plant, usually treated as containing just one species, ''Hydrilla verticillata'', though some botanists divide it into several species. It is native to the cool and warm waters of the Old World in ...

''. These all have leaves in whorls around the

stem Stem or STEM may refer to: Plant structures * Plant stem, a plant's aboveground axis, made of vascular tissue, off which leaves and flowers hang * Stipe (botany), a stalk to support some other structure * Stipe (mycology), the stem of a mushro ...

; however, ''Elodea'' usually has three leaves per whorl, whereas ''Egeria'' and ''Hydrilla'' usually have four or more leaves per whorl. ''Egeria densa'' is also a larger, bushier plant with longer leaves.Native Freshwater Plants
American Waterweed

Cultivation and uses

It is frequently used as an

aquarium An aquarium (plural: ''aquariums'' or ''aquaria'') is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aq ...

plant. Propagation is by cuttings.Hiscock, P. (2003). ''Encyclopedia of Aquarium Plants'' Interpret Publishing, United States and Canada . It is an

invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...

in Europe, Asia, Africa, and Oceania. It was introduced into

County Down County Down () is one of the six counties of Northern Ireland, one of the nine counties of Ulster and one of the traditional thirty-two counties of Ireland. It covers an area of and has a population of 531,665. It borders County Antrim to the ...

, Ireland in about 1836, and appeared in Great Britain in 1841, spreading through both countries in ponds, ditches and streams, which were often choked with its rank growth.Flora of NW Europe
''Elodea canadensis''
Other common names for this plant include ''Anacharis'' (an older name for the genus ''Elodea''), water thyme, common elodea, and ditch moss.

Gallery

Image:ElodeaCanadensisFlowering.jpg, Ditch with a dense colony of flowering plants Image:Elodea canadensis nf.jpg, Illustration showing leaf and flower detail Image:ElodeaLeaffaceupcells.jpg, Leaf cells at 450x magnification

References

{{Taxonbar, from=Q159760 Hydrocharitaceae Freshwater plants Flora of North America Plants described in 1803 Dioecious plants