Marsh-marigold (Caltha palustris), also known as 'kingcups' is a medium-sized member of the buttercup family Ranunculaceae. Growing up to 80cm high, this colourful plant is found in wet meadows, marshes and wet woodlands, and grows particularly well in the shade. Its flowers are quite large - between 15-50mm in diameter, and it is one of the early flowering plants, with flowers appearing in March and lasting until June/July. In autumn, the plants die back down and overwinters with buds near the surface fo the marshy soil.

Marsh-marigold (Caltha palustris) growing along the broad at UEA.

In terms of its ecology, Marsh-marigold only grows in freshwater locations with oxygen-rich water near the surface of the soil. It is quite a good bioindicator of pollution as it avoids areas with fertiliser application and high levels of phosphate and ammonia. However, it is often associated with iron-rich seepages because iron reacts with phosphate, thus making it unavailable for plants. In the UK, Marsh-marigold is quite widespread and its population remains fairly stable, however, it is locally threatened by drainage and agricultural improvement of wet grassland habitats.

C. palustris is an extremely variable species, with many different combinations of its features having been observed. There are however, 5 main varieties that are widely recognised:
  1. C. palustris var palustris which has yellow sepals, tricolpate pollen (pollen with 3 furrows) and is not rooting at the nodes. 
  2. C. palustris var radicans which also has yellow sepals and tricolpate pollen, but is distinguished by the plants being smaller and with fewer flowers on the stems as well as rooting at the nodes after flowering.
  3. C. palustris var araneosa also has yellow sepals and tricolpate pollen, however the plants are larger, and have many flowers on the stem and only occurs in the fresh water tidal zones of the Netherlands.
  4. C. palustris var alba has white sepals, usually pantoporate (with rounded opening all over the surface) pollen (although sometimes tricolpate), and is only found between 2200 and 3500m along rivulets in Afghanistan, Pakistan and the western Himalayas.
  5. C. palustris var purpurea has magenta sepals, tricolpate pollen and is only found between 4000-5000m on alpine meadows and mossy slopes in the eastern Himalayas.

Despite some serious safety concerns, people use the flowering parts of Marsh-marigold that live above ground to try and treat a variety of ailments, including cramps, jaundice and liver problems. Some people also put Marsh-marigold directly on the skin to clean wounds and sores. However, there is no evidence that Marsh-marigold actually works to treat any of these conditions and as with all buttercups it is poisonous and can cause skin irritation, so you shouldn't try it at home!

Marsh-marigold (Caltha palustris) with a Hoverfly species assisting with pollination.

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