Pennyworts
What are they?
The pennyworts are currently placed in the aralia family (Araliaceae) but at times they have been considered to be members of the carrot family (Apiaceae). There are many similarities between the two families in the way that the flowers are arranged, with pennyworts seemingly sharing some features from both families. These plants can be identified by their rounded leaves that are typically joined to their stems at the centre of the leaf blade - this is referred to as perfoliate. They have tiny, five-petalled flowers that can often be hard to find, or even lacking for much of the time and which are followed by flattened, paired fruits which are very like those of the carrot family.
Note that the leaves are similar to those of the navelworts, which are also sometimes called pennyworts (though not related) and can be compared by clicking here.
Where are they found?
These are plants of wetlands, typically growing in more or less permanently wet meadows and fens, or beside ponds, lakes and other waterways.
Identification
We have only one native species which makes identification fairly straightfoward as it is generally the only species likely to be found in wetland habitats that has perfoliate leaves (though beware of superficially similar water-crowfoots). Floating Pennywort is potentially a serious alien invasive and a threat to good quality habitats. It occurs from time to time in the wider countryside but its invasive threat is taken seriously and it is quickly removed by the Environment Agency - thus it is (as yet!) not a permanent feature of our wetlands.
Marsh Pennywort Hydrocotyle vulgaris
Native. A plant of permanently wet fens and bogs and beside permanent water bodies. Flowers June to July. A small, trailing or creeping plant that is often well hidden beneath taller vegetation. Leaves 1-3cm across. Flowers tiny, about 3mm across, appearing on short spikes with 1-3 whorls of flowers and usually hidden beneath the leaves.
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Floating Pennywort Hydrocotyle ranunculoides
Introduced from North America as an aquatic plant for garden ponds. Rapidly takes over small ponds, resulting in the pond-owners removing it and dumping it into natural waterways, where it has the potential to do great harm to a balanced ecosystem. Has appeared over time in a handful of locations but is typically removed by Environment Agency staff as soon as possible. Flowers June to July. Stems may be free-floating on open water and grow very rapidly, but typically do not flower. Stems on marginal mud root at the nodes and are typically the stems that produce flowers. Leaves can be larger than those of our native species, growing to around 8cm across.
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