Mentha aquatica is a perennial plant

Perennial plant

A perennial plant or simply perennial is a plant that lives for more than two years. The term is often used to differentiate a plant from shorter lived annuals and biennials. The term is sometimes misused by commercial gardeners or horticulturalists to describe only herbaceous perennials...

 in the genus Mentha

Mentha

Mentha is a genus of flowering plants in the family Lamiaceae . The species are not clearly distinct and estimates of the number of species varies from 13 to 18. Hybridization between some of the species occurs naturally...

native throughout Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 except for the extreme north, and also northwest Africa

Africa

Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

 and southwest Asia

Asia

Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

.

It is a herbaceous

Herbaceous

A herbaceous plant is a plant that has leaves and stems that die down at the end of the growing season to the soil level. They have no persistent woody stem above ground...

 rhizomatous perennial plant

Perennial plant

A perennial plant or simply perennial is a plant that lives for more than two years. The term is often used to differentiate a plant from shorter lived annuals and biennials. The term is sometimes misused by commercial gardeners or horticulturalists to describe only herbaceous perennials...

 growing to 90 centimetres (35.4 in) tall. The stems are square in cross section, green or purple, and variably hairy to almost hairless. The rhizome

Rhizome

In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

s are wide-spreading, fleshy, and bear fibrous root

Root

In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...

s. The leaves

Leaf

A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....

 are ovate to ovate-lanceolate, 2 to 6 cm (0.78740157480315 to 2.4 in) long and 1 to 4 cm (0.393700787401575 to 1.6 in) broad, green (sometimes purplish), opposite, toothed, and vary from hairy to nearly hairless. The flower

Flower

A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...

s are tiny, densely crowded, purple, tubular, pinkish to lilac in colour; flowering is from mid to late summer. Water Mint is pollinated by insects, and also spreads by underground rhizomes, like other species of mint. All parts of the plant have a distinctly minty smell.

As the name suggests, Water Mint occurs in the shallow margins and channels of streams, rivers, pools, dikes, ditches, canals, wet meadows, marshes and fens. If the plant grows in the water itself, it rises above the surface of the water. It generally occurs on mildly acid to calcareous

Calcareous

Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...

 (it is common on soft limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

) mineral or peat

Peat

Peat is an accumulation of partially decayed vegetation matter or histosol. Peat forms in wetland bogs, moors, muskegs, pocosins, mires, and peat swamp forests. Peat is harvested as an important source of fuel in certain parts of the world...

y soils. M. aquatica can occur in certain fen-meadow

Fen-meadow

A Fen-meadow is a habitat that occurs in numerous locations throughout northern and western Europe. This habitat is found in generally damp lowland areas....

 habitat

Habitat

* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

s such as the Juncus subnodulosus-Cirsium palustre plant association.

It hybridises with Mentha spicata (Spearmint) to produce Mentha × piperita

Peppermint

Peppermint is a hybrid mint, a cross between the watermint and spearmint . The plant, indigenous to Europe, is now widespread in cultivation throughout all regions of the world...

(Peppermint), a sterile hybrid; with Mentha suaveolens (Apple Mint) to produce Mentha × suavis; with Mentha arvensis

Mentha arvensis

Mentha arvensis is a species of mint with a circumboreal distribution. It is native to the temperate regions of Europe and western and central Asia, east to the Himalaya and eastern Siberia, and North America.It is a herbaceous perennial plant growing to 10–60 cm tall...

(Corn Mint) to produce Mentha × verticillata; and with both M. arvensis and M. spicata to give the tri-species hybrid Mentha × smithiana.