Floating Pennywort - Invasive Species Information

What Is Floating Pennywort - (Hydrocotyle ranunculoides)?

Habitat: Aquatic, waterways, ponds and ponds
Distribution in Ireland: Sparse distribution but locally abundant in some places.

Status: Established
Family name: Apiaceae.

Reproduction: Vegetative growth can be very rapid, with floating mats extending up to 20 cm per day its growth rate is highest in the summer months June and July.

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Floating pennywort Native to North and South America and parts of Africa and is an aquatic plant in the family Apiaceae.  In Ireland it is an invasive alien species which is currently spreading in waterways. Floating 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.

How To Identify Floating Pennywort?

Colour: Flowers are small, pale greenish white to pale yellow, and come in umbels of 5–13. Fruits are small achenes that can float, helping the seeds to disperse

Why Is Floating Pennywort A Problem?

competes with many native plant species. which are overgrown and shaded out by the extensive beds or floating carpets. Species richness of native aquatic plants may be reduced and submerged species may even disappear entirely. Floating pennywort can cause major problems in nature reserves, recreation areas and intensely managed waterways.

The floating mats not only affect the penetration of light available for photosynthesis, but also reduce oxygen levels in the water column which can result in fish mortality and influence invertebrate life, leading to sediment anoxia, the release of nutrients and potentially toxic substances can be enhanced.

Rapid biomass accumulation fuels decomposition processes, alters the composition of the bottom substrate and expedites the infilling of shallow standing waters. In flowing waters, drainage is impeded and siltation increases with heavy infestation.