''Hydrocotyle ranunculoides'', known commonly as floating pennywort, or floating marshpennywort, is an aquatic plant in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Apiaceae Apiaceae or Umbelliferae is a family of mostly aromatic flowering plants named after the type genus '' Apium'' and commonly known as the celery, carrot or parsley family, or simply as umbellifers. It is the 16th-largest family of flowering plan ...

. It is

native Native may refer to: People * Jus soli, citizenship by right of birth * Indigenous peoples, peoples with a set of specific rights based on their historical ties to a particular territory ** Native Americans (disambiguation) In arts and entert ...

to North and South America.

Origin and invasiveness

Water pennywort is an aquatic plant, native to the Americas. Due to its popularity as a pond plant, and subsequent escape into rivers, it has established as an

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

in parts of Europe, Australia, Africa and Japan. It was one of five aquatic plants which were banned from sale in the UK from April 2014, and was the first prohibition of its kind there. On the other hand, it is in decline in parts of its range in the United States. In Europe, floating pennywort is included since 2016 in the list of Invasive Alien Species of Union concern (the Union list). This implies that this species cannot be imported, cultivated, transported, commercialized, planted, or intentionally released into the environment in the whole of the European Union.

Description

Water pennywort has stems that spread horizontally and can float on water. Leaves grow on petioles up to 35 cm long, and are round to kidney-shaped, with 3–7 lobes and crenate to entire margins. Flowers are small, pale greenish white to pale yellow, and come in

umbel In botany, an umbel is an inflorescence that consists of a number of short flower stalks (called pedicels) that spread from a common point, somewhat like umbrella ribs. The word was coined in botanical usage in the 1590s, from Latin ''umbella'' "p ...

s of 5–13. Fruits are small achenes that can float, helping the seeds to disperse. The South American

weevil Weevils are beetles belonging to the superfamily Curculionoidea, known for their elongated snouts. They are usually small, less than in length, and herbivorous. Approximately 97,000 species of weevils are known. They belong to several families, ...

Listronotus elongatus ''Listronotus elongatus'' is a weevil native to South America, of the genus of underwater weevils '' Listronotus''. It lays eggs on and eats the invasive floating pennywort ('' Hydrocotyle ranunculoides''). The larvae also eat into the stems, re ...

'' lays eggs on and eats the floating pennywort, and larvae also eat into the stems, reducing the pennywort's ability to grow. The weevil has been introduced for

biocontrol Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also in ...

of the floating pennywort into waterways in Britain, following extensive research to establish that the weevil is not a threat in itself.

References

ranunculoides Flora of North America Flora of South America Taxa named by Carl Linnaeus Flora without expected TNC conservation status {{Araliaceae-stub