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Floating marsh pennywort

(Hydrocotyle ranunculoides)

Photo of floating marsh pennywort

Extremely fast-growing floating aquatic plant, can grow up to 20 cm per day and 15 m from the bank in a single season and can double its biomass in 3 to 7 days.


Other names for this plant include:
  • Common names: floating pennywort, marsh pennywort, water pennywort
  • Scientific names: Hydrocotyle natans, Hydrocotyle cymbalarifolia, Hydrocotyle batrachioides, Hydrocotyle ranunculoides forma lobata, Hydrocotyle ranunculoides forma genuina
Ecological threat:
  • It invades freshwater lakes, reservoirs, ponds, marshes and slow-flowing streams and rivers making boating, fishing and almost all other water activities difficult.
  • Degrades water quality by blocking the air-water interface and greatly reducing oxygen levels in the water, impacting underwater animals such as fish.
  • Greatly reduces biological diversity: mats block sunlight, preventing the growth of submerged and emersed plant communities and also alter animal communities by blocking access to the water and/or reducing plants the animals depend on for shelter and nesting.
 Overview map of prohibited classification in WI
Prohibited (red) counties

Classification in Wisconsin: Prohibited

Species Assessment Groups (SAG) were assembled to recommend a legal classification for each species considered for NR 40. The recommendation for floating marsh pennywort was based upon this literature review [PDF] developed by the department.


Leaves: 2-6 cm in diameter, rounded or wider than long, with 3-7 lobes. The lobe divisions extend to about mid-leaf. The leaf edges are smooth to slightly scalloped. Slender stalks 5-35 cm long are attached to the leaf edge, although the stalk may appear to be attached to the center of the leaf.

Flowers: very small creamy yellow flowers (usually 9) approximately 3 mm in diameter on a short umbel below the leaf canopy.

Fruits & seeds: The fruit is 1-3 mm long, elliptic to round and flattened with faint ribs. It is divided into 2 halves, each with a tiny persistent stalk.

Roots: Fine fibrous roots that can penetrate the soil or drift in the water from the stem at nodes.

Similar species: Could be mistaken for other Hydrocotyle or Ranunculus species.


Mechanical: Removal by hand or machine is a practical control method often used for small areas or when numbers are low. Physical removal should be completed before the flowering and seed set. Care should be taken to collect and destroy all parts of the plants.

Chemical: Registered aquatic herbicides can provide some control in small scale applications. Application of aquatic herbicide requires a permit.


View floating marsh pennywort in our photo gallery!


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